3.8: Introductions
- Identify successful strategies for writing introductions
Just because the introduction appears first in an essay, doesn’t mean it has to be written that way. Good writing is a recursive process and even when a writer does construct an initial introduction at the beginning of the writing process, they will return to it frequently to see how it fits with the rest of the piece. Regardless of when the introduction is composed, it is important to make it a good one because the introduction sets the stage for the rest of the essay.
Introductions
Even though a nearly infinite number of topics and arrangements are possible in English prose, introductions generally follow one of several patterns. If you’re writing a children’s story, you’d probably start with “once upon a time” or something similar. If you’re writing a research article on biomechanical engineering, you’d probably start with a statement about how previous research has examined the problem of loading soldiers with daypacks on various surfaces, including sand, concrete, and railroad ballast. These examples are poles apart, but their introductions share very similar purposes: they orient their imagined readers to the topic, time, and place.
Many students make the mistake of beginning their essays in overwhelmingly broad or obvious terms. For example, a student writing about the politics of same-sex marriage might begin a paper by saying, “People have been falling in love and getting married for thousands of years.” A sentence like this simply postpones the real work of an essay by giving its audience information that any reasonable person would already know. Students usually write overly vague introductions because they have been taught to “start broad” and then “narrow their focus.” More experienced writers understand that everything in an introduction needs to contribute substantially to their argument.
There is no strict formula for composing an introduction, but effective introductions often do the following:
- Provide background about a topic
- Locate readers in a specific time and/or place
- Start with a compelling quotation or statistic—something concrete
- Include an ethical appeal, with which you (explicitly or implicitly) show that you’ve researched your topic and are credible
- Articulate a main claim/thesis (but normally after some buildup)
- Layout the stakes for the piece of writing—that is, why the reader should bother reading on
Sample Introductions
Let’s look at some examples of introductions:
The introduction below provides background information and a compelling quotation or statistic. In the following example, notice how just a few sentences can offer background and make the thesis of the essay clear:
- In the early twentieth century, there were just 8,000 cars in the United States and only 144 miles of paved roads. In 2005, the Department of Transportation recorded 247,421,120 registered passenger vehicles in the United States and more than 5.7 million miles of paved highway. The automobile has changed our way of life dramatically in the last century.
The next introduction makes an argument about the role of a musical instrument in 245 BCE by locating readers in a specific time and/or place.
- In 246 BCE, Ctesibius of Alexandria invented a musical instrument that would develop into what we know as the organ. Called a hydraulis, it functioned via wind pressure regulated by means of water pressure. The hydraulis became the instrument played at circuses, banquets, and games throughout Mediterranean countries.
Students often want to know how many sentences an introduction should be. There is no magic formula although some writing instructors have particular guidelines or preferences.
The example below is a single sentence introduction that could work as a very short introduction to a brief paper or could be expanded for a longer essay.
- While IQ tests have been used for decades to measure various aspects of intelligence, these tests are not a predictor of success, as many highly intelligent people have low emotional intelligence, the important human mental ability to reason about emotions and to use emotions to enhance thought.
Notice how this brief introduction packs a great deal of information into one sentence (not always a recommended strategy) but still manages to articulate a main claim/thesis (that IQ tests are not a predictor of success) while also explaining how the tests have been used and why they may be misleading.
The longer introduction below moves from the image of a six-year-old playing with Barbies to a strong thesis about the benefits of pageants.
- When most people think of normal activities for a six-year-old girl, they picture a sea full of Barbie dolls, coloring books and dress-up clothes. Popular shows such as “Toddlers and Tiaras,” which revolves around exaggerated filming of child pageantry, show America one narrow view of what the pageant world is all about. The media distorts how society views pageants, but, in fact, pageants can be viewed on the same positive level as other popular competitive sports. Pageants can be beneficial because they give children contestants useful life lessons.
Keep in mind that some of the examples above are too short to function as complete introductions and are offered to help you think about how you might get your introduction started.
Strategies for Good Introductions
Although there is no one “right” way to write your introduction, there are some common introductory strategies that work well. The strategies below are ones you should consider, especially when you are feeling stuck and having a hard time getting started.
Consider opening with an interesting fact, an anecdote, a pithy quotation, an image, or a question to provoke your reader’s interest.
One technique is to provide information or data that draw the audience’s attention to the problem or issue. To present her research on electric car usage and ownership, Yuliya Chernova writes:
- Electric cars are still such a novelty that little is known about their owners and how they use the vehicles. But recent research is beginning to unlock some of the mysteries. Plug-in vehicles—those that run entirely on battery power or that combine electric and gasoline drives—represent less than 1% of total U.S. vehicle sales, but in the past three years their numbers have grown rapidly. Sales nearly tripled in 2012 and are on track to nearly double this year, according to the Electric Drive Transportation Association, a trade group. (Chernova, 2013)
Consider employing anecdotes that dramatize the problem or issue. Brad Tuttle begins his article, ”The Major Problem with Cheap Electric Cars,” with the following account:
- Mitsubishi is the latest in a long line of automakers to slash prices on an electric car, the unpronounceable, unfortunately named i-MiEV. The model is now the cheapest electric vehicle (EV) on the market, yet it’s still hard to imagine many drivers excitedly running out to buy one. (Tuttle, 2013)
Another strategy is to respond to a quotation that addresses the problem or issue in some way. Columnist George F. Will quotes President Barack Obama to begin his own argument about the United States’ policy on Iran’s nuclear program:
- In his disproportionate praise of the six-month agreement with Iran, Barack Obama said: “For the first time in nearly a decade, we have halted progress of the Iranian nuclear program.” But if the program, now several decades old, had really been “halted” shortly after U.S. forces invaded neighboring Iraq, we would not be desperately pursuing agreements to stop it now, as about 10,000 centrifuges spin to enrich uranium. (Will, 2013)
Overall, your focus in an introduction should be on orienting your reader. Notice how the example below catches the reader’s attention with references to the game Atari and the television show Dynasty and closes with a strong, clear thesis.
- Play Atari on a General Electric brand television set? Maybe watch Dynasty ? Or read old newspaper articles on microfiche at the library? Twenty-five years ago, the average college student did not have many options when it came to entertainment in the form of technology. Fast-forward to the twenty-first century, and the digital age has digital technology, consumers are bombarded with endless options for how they do most everything-from buying and reading books to taking and developing photographs. In a society that is obsessed with digital means of entertainment, it is easy for the average person to become baffled. Everyone wants the newest and best digital technology, but the choices are many and the specifications are often confusing.
Remember, an effective introduction will capture your reader’s attention, provide context for your topic, and transition to your thesis.
Contributors and Attributions
- Writing Introductory and Concluding Paragraphs. Provided by : Minnesota Libraries Publishing. Located at : https://open.lib.umn.edu/writingforsuccess/chapter/9-4-writing-introductory-and-concluding-paragraphs/ . Project : Writing for Success. License : CC BY-NC-SA: Attribution-NonCommercial-ShareAlike
- Introductions. Provided by : Excelsior College. Located at : http://owl.excelsior.edu/writing-process/introductions-and-conclusions/ . Project : Excelsior OWL. License : CC BY: Attribution
- Image of fishing line. Authored by : Free-Photos. Provided by : Pixabay. Located at : pixabay.com/photos/fly-fishing-fishing-rod-fishing-rod-1149502/. License : Other . License Terms : pixabay.com/service/terms/#license
- Sample paragraph, Approaches to Written Argument . Provided by : Radford University. Located at : https://lcubbison.pressbooks.com/chapter/core-101-opposing-viewpoints/ . Project : Radford University Core Handbook. License : Public Domain: No Known Copyright
- How do I introduce a topic and explain its significance. Provided by : Radford University. Located at : https://lcubbison.pressbooks.com/chapter/core-101-academic-argument-essay/ . Project : Radford University Core Handbook. License : Public Domain: No Known Copyright


7.2: The Decision-making Process
For major life decisions such as choosing a major/career or deciding on your transfer college, using a logical and ordered process allows us to make effective decisions. The decision-making process we will use in this class involves the following five steps (Martinez & Shaker, 2021).
- Step 1: Formulating a goal or goals
- Step 2: Identifying the background information needed for making decisions
- Step 3: Identifying alternatives
- Step 4: Performing analysis
- Step 5: Making a final decision
These steps provide structure and discipline for the process of making serious decisions. Each step requires you to be proactive while brainstorming, investigating information, collecting and analyzing data and then taking effective action (University of Minnesota Libraries Publishing, 2010).
Application of the Decision-making Process
Let’s apply the steps involved in this decision-making process:
Step 1: Formulating a goal or goals
This step involves assessing the current situation and defining your goal. Ask yourself:
- What do you want to accomplish?
- Is the current situation a problem to solve or an opportunity to pursue? Knowing the difference will help guide you through the remaining steps and will help you organize your support network.
Here’s an example that may reflect a student in this class: “I have finished my career assessments and taken time to conduct career research. I now have four career options I am considering but don’t know which to pursue. I learned I am passionate about pursuing a career in the helping profession but can’t decide between elementary school teaching, social work, nursing or school counselor. These all are possible opportunities for me to pursue!
My goal is to determine which career path is best for me and how I can get there.
Step 2: Identifying the background information needed for making the decision
This step involves doing research and gathering relevant information. Ask yourself:
- What information do you currently know about your options?
- What information is missing?
- What sources will help you learn more about your options and who can help you gather more information?
Applying Step 2 to the example above:
- I am familiar with online career research sites addressed in this text. I might consider putting together a chart where I can take notes and do a side-by-side comparison among these different occupations including duties and responsibilities, educational training, licensing/certification requirements, salary information and current labor market trends and job outlook.
- I can arrange for informational interviews with professionals in each of the careers I am considering to gain a more personalized perspective on each profession.
- I can meet with an advisor to get an overview of the different majors that may be a good fit, develop an educational plan and compare and contrast the different options as well as transfer options.
Step 3: Identifying alternatives
On a journey, usually there are many roads that get to one place. This step allows you to put together as many creative options as possible based on the information gathered in Step 2. As you develop your options, consider possible obstacles and challenges you may foresee so you can plan and seek necessary support to help overcome those obstacles and challenges.
Applying Step 3 to the example above:
As I conducted my research four options stood out to me:
- elementary school teacher
- social worker
- guidance counselor
- nurse
Step 4: Performing analysis
As you identify alternatives, assess yourself and your current situation to see which of the options seems most attractive to you at this time. This step allows you to dive deep and evaluate alternatives, assess the outcomes of each option and consider how they align with your values to help you narrow down your options. Consider ranking your options and focus on your first choice. Assess your likelihood of success toward each alternative and consider sacrifices you may need to make. Revisit any possible challenges or obstacles you may foresee and address any barriers that may affect your success.
Applying step 4 to the example above:
Now I can start putting together and analyzing how the information fits my current situation and needs. After gathering the career information and speaking to professionals in the field, I feel strongly that being an elementary school teacher best aligns with my values and allows me to focus on making a difference while helping children learn and grow. This career aligns nicely with my personality preferences, values, interests, character strengths, skills and abilities. My career assessments confirm this path is a suitable option for me. I now will pursue elementary school teaching as my focus!
My research also tells me that the most likely major is Early Childhood Elementary Education, but depending on my intended transfer college, I may want to major in General Education. I’ll check with my advisor about the best major at HACC to prepare me for transfer to my intended transfer college.
Step 5: Making a final decision
Now you are ready to establish a plan of action. This step involves putting together necessary steps to pursue your desired outcome. Set a date you will start and complete your plan of action. Be realistic as you develop your plan. Consider resources you will need to put your plan into action.
Applying step 5 to the example above:
After researching the classes required for each major, I decided to pursue Early Childhood Education because this major does not require as much science and allows me to focus on child growth and development and how children learn which is more interesting to me. Now that I have narrowed down my options and decided on a path, I am ready to develop my plan of action!
Next semester, I will:
- Enroll in EDUC 110 - Foundations of PK-4 Education and see how I like the class.
- Meet with an advisor to change my major, establish my educational plan and review requirements for my associate degree and transfer.
- Talk to my education advisor and start networking!
The decision-making model described above is linear in nature where one step leads to the next, but please note that you may revisit a previous step at any time throughout the process. For example, after completing Step 4 and analyzing the situation, you may realize the alternatives generated in Step 3 are not of interest to you anymore so you may need to go back to Step 2 and gather more information before moving forward ((University of Minnesota Libraries Publishing, 2010).
Be flexible and open to change. Be patient and know that you are not alone on this journey. There is a lot of support on campus to help you brainstorm, gather information and evaluate your options. You always have options!
Once you decide upon a career, your decision will guide the goals you set for yourself from your college education to your future career. For help to stay on track in this journey, you can seek assistance from the information and resources you learn in this class as well as advisors and Career Services staff at the college to guide your search.
Internal and External Factors that Affect Decision-making
There are many factors that contribute to making decisions, some internal and some external. Internal factors are those you control because they come from within you. Internal factors are influenced by your feelings and thoughts, both positive or negative. Positive thoughts will help you with decision-making, while negative thoughts most likely will hinder you. Fear is a common internal factor that negatively affects decision-making (University of Minnesota, 2010).
- Fear of failure
- Fear of making the wrong decision
- Fear of rejection
- Fear of letting others down
Unfortunately, fear can lead to paralysis in the decision-making process with “worse case scenarios.” To avoid this paralysis, remember FEAR is an acronym for:
F alse E xpectation A ppearing R eal
Remember, you are in control of these internal thoughts and feelings in terms of your mindset (discussed earlier in this text). Your internal thoughts and feelings hold a lot of power over your actions so use that power wisely by maintaining a growth mindset. If you have a growth mindset, even though you may have fear, you will believe you are capable of making effective decisions.
Another internal factor that affects decision-making is self-confidence. Lack of self-confidence can make decision-making challenging and negatively impact your goals. Earlier in this text we addressed the importance of self-confidence in setting yourself up for success. You can be your best friend through the decision-making process or your worst enemy. The choice is up to you. If you lack self-confidence, the good news is you can work on building self-confidence and self-efficacy and developing your growth mindset.
External factors are those that stem from your surroundings. External factors may include expectations from your family, friends, cultural or gender stereotypes and family responsibilities. You also may need to consider factors such as your finances, where you live and the timing of this decision relative to other life goals and commitments. External factors can influence decision-making in a positive or negative way. Considering external factors when making decisions is important so you can absorb the positive support and create a plan to counteract the negative (University of Minnesota, 2010).
Also, remember the discussion of career priorities earlier in this text. Your career priorities involve both internal and external factors and guide your career decision-making. After making a decision about your career direction, you need to be mindful of the internal and external factors that may affect your next steps. Once you have narrowed down your career choices, you will set a long-term goal and develop a plan of action by setting effective short- and mid-term goals leading to the long-term goal.
My Decision-making Style
When it comes to making a decision regarding your career, what internal and external factors are affecting your decision process?
Internal Factors
- __________________________________________________________________
- __________________________________________________________________
- __________________________________________________________________
External Factors
- __________________________________________________________________
- __________________________________________________________________
- __________________________________________________________________


18.8: Magnetic Forces in a Conductor - The Hall Effect
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Learning Objectives
By the end of this section, you will be able to:
- Explain a scenario where the magnetic and electric fields are crossed and their forces balance each other as a charged particle moves through a velocity selector
- Compare how charge carriers move in a conductive material and explain how this relates to the Hall effect
In 1879, E.H. Hall devised an experiment that can be used to identify the sign of the predominant charge carriers in a conducting material. From a historical perspective, this experiment was the first to demonstrate that the charge carriers in most metals are negative.
Visit this website to find more information about the Hall effect.
We investigate the Hall effect by studying the motion of the free electrons along a metallic strip of width l in a constant magnetic field (Figure \(\PageIndex{1}\)). The electrons are moving from left to right, so the magnetic force they experience pushes them to the bottom edge of the strip. This leaves an excess of positive charge at the top edge of the strip, resulting in an electric field E directed from top to bottom. The charge concentration at both edges builds up until the electric force on the electrons in one direction is balanced by the magnetic force on them in the opposite direction. Equilibrium is reached when:
\[eE = ev_d B \label{11.24} \]
where e is the magnitude of the electron charge, \(v_d\) is the drift speed of the electrons, and E is the magnitude of the electric field created by the separated charge. Solving this for the drift speed results in
\[v_d = \frac{E}{B}. \label{11.25} \]
A scenario where the electric and magnetic fields are perpendicular to one another is called a crossed-field situation. If these fields produce equal and opposite forces on a charged particle with the velocity that equates the forces, these particles are able to pass through an apparatus, called a velocity selector , undeflected. This velocity is represented in Equation \ref{11.26}. Any other velocity of a charged particle sent into the same fields would be deflected by the magnetic force or electric force.
Going back to the Hall effect, if the current in the strip is I , then from Current and Resistance , we know that
\[I = nev_dA \label{11.26} \]
where n is the number of charge carriers per volume and A is the cross-sectional area of the strip. Combining the equations for \(v_d\) and I results in
\[I = ne\left(\frac{E}{B}\right)A. \label{11.27} \]
The field E is related to the potential difference V between the edges of the strip by
\[E = \frac{V}{l}. \label{11.28} \]
The quantity \(V\) is called the Hall potential and can be measured with a voltmeter. Finally, combining the equations for I and E gives us
\[V = \dfrac{IBl}{neA} \label{hallV} \]
where the upper edge of the strip in Figure \(\PageIndex{1}\) is positive with respect to the lower edge.
We can also combine Equation \ref{11.24} and Equation \ref{11.28} to get an expression for the Hall voltage in terms of the magnetic field:
\[V = Blv_d. \nonumber \]
What if the charge carriers are positive, as in Figure \(\PageIndex{1}\)? For the same current I , the magnitude of V is still given by Equation \ref{hallV}. However, the upper edge is now negative with respect to the lower edge. Therefore, by simply measuring the sign of V , we can determine the sign of the majority charge carriers in a metal.
Hall potential measurements show that electrons are the dominant charge carriers in most metals. However, Hall potentials indicate that for a few metals, such as tungsten, beryllium, and many semiconductors, the majority of charge carriers are positive. It turns out that conduction by positive charge is caused by the migration of missing electron sites (called holes) on ions. Conduction by holes is studied later in Condensed Matter Physics .
The Hall effect can be used to measure magnetic fields. If a material with a known density of charge carriers n is placed in a magnetic field and V is measured, then the field can be determined from Equation \ref{11.29}. In research laboratories where the fields of electromagnets used for precise measurements have to be extremely steady, a “Hall probe” is commonly used as part of an electronic circuit that regulates the field.
Example \(\PageIndex{1}\): Velocity Selector
An electron beam enters a crossed-field velocity selector with magnetic and electric fields of 2.0 mT and \(6.0 \times 10^3 \, N/C\), respectively. (a) What must the velocity of the electron beam be to traverse the crossed fields undeflected? If the electric field is turned off, (b) what is the acceleration of the electron beam and (c) what is the radius of the circular motion that results?
Strategy
The electron beam is not deflected by either of the magnetic or electric fields if these forces are balanced. Based on these balanced forces, we calculate the velocity of the beam. Without the electric field, only the magnetic force is used in Newton’s second law to find the acceleration. Lastly, the radius of the path is based on the resulting circular motion from the magnetic force.
Solution
- The velocity of the unperturbed beam of electrons with crossed fields is calculated by Equation \ref{11.25}: \[v_d = \frac{E}{B} = \frac{6 \times 10^3 N/C}{2 \times 10^{-3} T} = 3 \times 10^6 m/s. \nonumber \]
- The acceleration is calculated from the net force from the magnetic field, equal to mass times acceleration. The magnitude of the acceleration is: \[ma = qvB \nonumber \] \[a = \frac{qvB}{m} = \frac{(1.6 \times 10^{-19}C)(3 \times 10^6 m/s)(2 \times 10^{-3}T)}{0.1 \times 10^{-31}kg} = 1.1 \times 10^{15} m/s^2. \nonumber \]
- The radius of the path comes from a balance of the circular and magnetic forces, or Equation \ref{11.25}: \[r = \frac{mv}{qB} = \frac{(9.1 \times 10^{-31}kg)(3 \times 10^6 m/s)}{(1.6 \times 10^{-19}C)(2 \times 10^{-3}T)} = 8.5 \times 10^{-3} m. \nonumber \]
Significance
If electrons in the beam had velocities above or below the answer in part (a), those electrons would have a stronger net force exerted by either the magnetic or electric field. Therefore, only those electrons at this specific velocity would make it through.
The Hall Potential in a Silver Ribbon
Figure \(\PageIndex{2}\) shows a silver ribbon whose cross section is 1.0 cm by 0.20 cm. The ribbon carries a current of 100 A from left to right, and it lies in a uniform magnetic field of magnitude 1.5 T. Using a density value of \(n = 5.9 \times 10^{28}\) electrons per cubic meter for silver, find the Hall potential between the edges of the ribbon.
Strategy
Since the majority of charge carriers are electrons, the polarity of the Hall voltage is that indicated in the figure. The value of the Hall voltage is calculated using Equation \ref{hallV}.
Solution
When calculating the Hall voltage, we need to know the current through the material, the magnetic field, the length, the number of charge carriers, and the area. Since all of these are given, the Hall voltage is calculated as:
\[\begin{align*} v &= \frac{IBl}{neA} \\[4pt] &= \frac{(100 \, A)(1.5 \, T)(1.0 \times 10^{-2}m)}{(5.9 \times 10^{28} /m^3)(1.6 \times 10^{-19}C)(2.0 \times 10^{-5}m^2)} \\[4pt] &= 7.9 \times 10^{-6}V. \end{align*} \nonumber \]
Significance
As in this example, the Hall potential is generally very small, and careful experimentation with sensitive equipment is required for its measurement.
Exercise \(\PageIndex{1}\)
A Hall probe consists of a copper strip, \(n = 8.5 \times 10^{28}\) electrons per cubic meter, which is 2.0 cm wide and 0.10 cm thick. What is the magnetic field when I = 50 A and the Hall potential is
- \(4.0 \, \mu V\) and
- \(6.0 \, \mu V\)?
- Answer a
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1.1 T
- Answer b
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1.6 T


5.10: Shapes of Distributions
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Learning Objectives
We saw in the section on distributions in Chapter 1 that shapes of distributions can differ in skew and/or kurtosis. This section presents numerical indexes of these two measures of shape.
Figure \(\PageIndex{1}\) shows a distribution with a very large positive skew. Recall that distributions with positive skew have tails that extend to the right.
Distributions with positive skew normally have larger means than medians. The mean and median of the baseball salaries shown in Figure \(\PageIndex{1}\) are \(\$1,183,417\) and \(\$500,000\) respectively. Thus, for this highly-skewed distribution, the mean is more than twice as high as the median. The relationship between skew and the relative size of the mean and median led the statistician Pearson to propose the following simple and convenient numerical index of skew:
\[\frac{3(Mean-Median)}{\sigma }\]
The standard deviation of the baseball salaries is \(1,390,922\). Therefore, Pearson's measure of skew for this distribution is \(\dfrac {3(1,183,417 - 500,000)}{1,390,922} = 1.47\).
Just as there are several measures of central tendency, there is more than one measure of skew. Although Pearson's measure is a good one, the following measure is more commonly used. It is sometimes referred to as the third moment about the mean.
\[\sum \dfrac {(X-\mu )^3}{\sigma ^3}\]
The following measure of kurtosis is similar to the definition of skew. The value "\(3\)" is subtracted to define "no kurtosis" as the kurtosis of a normal distribution. Otherwise, a normal distribution would have a kurtosis of \(3\).
\[\sum \dfrac {(X-\mu )^4}{\sigma ^4}-3\]


17.5: Going to College Is an Opportunity of a Lifetime—Never Drop Out
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You have already had one of your dreams come true—you are in college. It is indeed a rare privilege because far less than 1 percent of traditional college-age people around the world get to attend college. You’re lucky! So make the best of it by finishing your degree and learning the following college skills. 7
Learn to Concentrate
Concentration is the art of being focused, the ability to pay attention. Without concentration, you have no memory of what you hear, see, and read. Concentration is a frame of mind that enables you to stay centered on the activity or work you are doing. You know when you’re concentrating because time seems to go by quickly, distractions that normally take you off task don’t bother you, and you have a lot of mental or physical energy for the task.
You are ultimately in charge of how well you concentrate. Here are some ways to make it happen:
- Choose a workplace . Avoid the bed—you associate it with relaxing or sleeping. Try a desk or table for studying; you will concentrate better and accomplish more in less time. You will also have a convenient writing space and plenty of space to spread out. Be sure to have good lighting.
- Feed your body right. What you eat plays an important role in how well or how poorly you concentrate. Protein foods (such as cheese, meat, fish, and vegetables) keep the mind alert, while carbohydrates (such as pasta, bread, and processed sugars) make you sleepy. Caffeine (commonly found in coffee, tea, soft drinks, and chocolate) acts as a stimulant in low doses.
- Avoid food . Food and serious learning don’t mix well. Think about it. When you try to eat and study at the same time, which gets more of your concentration? The food, of course. You will be more effective if you eat first and then study.
- Listen to your own thoughts. Listening to anything but your own thoughts interferes with good concentration. Eliminating distractions such as music, television, cell phones, email and text beeps, and other people can greatly increase the amount of studying you can accomplish. Hold all calls, and let email and texts wait.
- Make a to-do list. If you are trying to study but get distracted by all of the things you need to do, take time to make a to-do list. Keeping track of your thoughts on paper and referring to the paper from time to time can be very effective for clearing your mind and focusing on your task.
- Take short, frequent breaks. Since people concentrate for about 20 minutes or less at a time, it would make sense to capitalize on your natural body rhythms and take a short break every 20 to 30 minutes. If you feel you are fully concentrating and involved in a task, then work until a natural break occurs.
Learn to Manage Your Time
There are two ways to make sure you have more time in a day. The first and most important way to gain more time is to plan it. It’s like getting in a car and going somewhere. You need to know where you are going and have a plan to get there. Without a plan, you will waste your time and take longer to get to your destination—if you get there at all!
A weekly project planner will allow you to keep track of your assignments in more detail. It contains a to-do list specific to one day. It looks like a calendar but is divided into five one-day periods with plenty of space to write. Using a weekly project planner is an effective way to keep track of assignments and plan study time according to the school calendar. Free calendars are available at https://calendar.google.com .
A second way to gain more time in a day is to do more in less time . This can be as simple as doubling up on activities. For example, if you have three errands, you might try to combine them instead of doing one at a time, making one round-trip instead of three. If you commute on a bus, on a train, or in a carpool, you can study during your ride. At lunch, you can review notes. Use your imagination as to how you can get more done in less time.
Here are some ideas to help you master your time:
- Prepare for the morning the night before. Put out your clothes; make lunches; pack your books.
- Get up 15 minutes earlier in the morning. Use the time to plan your day, review your assignments, or catch up on the news.
- Schedule a realistic day . Avoid planning for every minute. Leave extra time in your day for getting to appointments and studying.
- Leave room in your day for the unexpected. This will allow you to do what you need to do, regardless of what happens. If the unexpected never happens, you will have more time for yourself.
- Do one thing at a time. If you try to do two things at once, you become inefficient. Concentrate on the here and now.
- Learn to say “No.” Say no to social activities or invitations when you don’t have the time or energy.
How well do you manage your time? Take the quiz in Table 17.4 to find out.
Use Your Money Wisely
You can get college money from several different sources, including the following.
- Grants and Scholarships. This refers to aid you do not have to repay. Grants are usually based on need while scholarships are frequently based on academic merit or other qualifying factors.
- Educational Loans. These are usually subsidized by federal and state governments, private lenders, or the colleges themselves. Generally, the loans carry lower interest rates than commercial loans, and you do not have to pay them off until after graduation.
- Work Aid. This is financial aid you have to work for, frequently 10 or 15 hours a week on campus.
There are many ways to cut the cost of going to college. Consider these:
- Going to a community college for the first two years and then transferring to a four-year institution
- Attending a nearby college and living at home
- Enrolling in one of thousands of college and universities with cooperative educational programs that alternate between full-time studies and full-time employment
- Taking a full-time job at a company that offers free educational opportunities as an employee benefit
| Fun Self-Test—How Well Do You Manage Your Time? | ||||
|---|---|---|---|---|
| Rate your level of agreement with the following statements using the scale below: | ||||
| Strongly Agree | Agree | Neither Agree nor Disagree | Disagree | Strongly Disagree |
|
||||
| See the scoring guidelines at the end of this chapter to obtain your score. |
Table 17.4
To learn about college costs and financial aid, one of the first sources to consult is the website of The College Board, a not-for-profit organization that connects students to college success and opportunity. Some of the important topics covered at www.collegeboard.org include explaining financial aid, facilitating the application process, and finding colleges that fit. There are other websites that also offer information on financial aid:
- http://www.fastweb.com : Fastweb has a database of more than 1.5 million private-sector scholarships, grants, and loans.
- http://www.ed.gov : This is the U.S. Department of Education information site for federal aid programs, including student loans and grants.
Gain some insight into your money management skills by taking the quiz in Table 17.5 .
Study Well
The first key to doing well in a subject is to complete your assignments on time. Most instructors base their assignments on what they will be discussing in class on a given day. So, if you read the pages you are assigned for the day they are due, you will better understand the day’s lecture. If you don’t complete an assignment when it is due, not only will you be at a disadvantage in the class, but you will also have twice as much work to do for the following class.
Second, know what material to study. This may sound simple, but all too often students do not ask what material they should study and find out too late that they studied the wrong information. The easiest and most accurate way to learn what will be covered on a test is to ask your instructor or read the syllabus.
Tests measure your working memory and knowledge base. To help yourself remember, you can use several memory devices to recall the information you need to study. Here are a few memory devices that have been proven to work:
| Fun Self-Test—Are You Good at Managing Money? | ||||
|---|---|---|---|---|
| Rate your level of agreement with the following statements, using the scale below: | ||||
| Strongly Agree | Agree | Neither Agree nor Disagree | Disagree | Strongly Disagree |
|
||||
| See the scoring guidelines at the end of this chapter to obtain your score. |
Table 17.5
- Recite information using your own words. You will learn more when you reinforce your learning in as many ways as possible. You can reinforce your learning through hearing, writing, reading, reviewing, and reciting.
- Develop acronyms. Acronyms are words or names formed from the first letters or groups of letters in a phrase. Acronyms help you remember because they organize information according to the way you need or want to learn it. For example, COD means “cash on delivery,” and GDP refers to “gross domestic product.” When you study for a test, be creative and make up your own acronyms.
-
Try mnemonic sentences, rhymes, or jingles.
Mnemonic sentences are similar to acronyms; they help you organize your ideas. But instead of creating a word, you make up a sentence. Creating a rhyme, song, or jingle can make the information even easier to remember. The more creative and silly the sentence, the easier it is to remember. Take, for example, the nine planets listed in order according to their distance from the sun:
M ercury V enus E arth M ars J upiter S aturn U ranus N eptune
The first letters of these words are: M V E M J S U N .
An acronym using these letters would be difficult to remember. But if you create a sentence using the letters in order, you will remember the sequence better. For example: M y V ery E ducated M other J ust S erved U s N ine P izzas.
- Visualize. Visualization refers to creating or recalling mental pictures related to what you are learning. Have you ever tried to remember something while taking a test and visualized the page the information was on? This is your visual memory at work. Approximately 90 percent of your memory is stored visually in pictures, so trying to visualize what you want to remember is a powerful study tool.

Become a Master at Taking Tests
Taking a formal test is like playing a game. The object is to get as many points as possible in the time you are allowed. Tests are evaluations of what you know and what you can do with what you know. Here are the rules of the test-taking game:
- Rule 1: Act As If You Will Succeed. Thought is powerful. When you think negative thoughts, your stress level rises. Your confidence level may drop, which often leads to feelings of failure. When this happens, think about success. Smile and take deep, slow breaths. Close your eyes, and imagine getting the test back with a good grade written at the top.
| Fun Self-Test—Do You Have Good Study Habits? |
|---|
| Answer “yes” or “no” to the following questions: |
|
| See the scoring guidelines at the end of this chapter to obtain your score. |
Table 17.6
- Rule 2: Arrive Ahead of Time. Being on time or early for a test sets your mind at ease. You will have a better chance of getting your favorite seat, relaxing, and preparing yourself mentally for the game ahead.
- Rule 3: Bring the Essential Testing Tools. Don’t forget to bring the necessary testing tools along with you, including extra pens, sharpened pencils, erasers, a calculator, laptop, dictionary, and other items you may need.
- Rule 4: Ignore Panic Pushers. Some people become nervous before a test and hit the panic button, afraid they don’t know the material. Panic pushers are people who ask you questions about the material they are about to be tested on. If you know the answers, you will feel confident; however, if you don’t, you may panic and lose your confidence. Instead of talking with a panic pusher before a test, spend your time concentrating on what you know, not on what you don’t know.
-
Rule 5: Preview the Playing Field.
Here’s how to do a preview:
- Listen to instructions, and read directions carefully.
- Determine the point spread. Look at the total number of questions and the point value of each. Decide how much time you can spend on each question and still finish the test on time.
- Budget your time. If you budget your time and stick to your time limits, you will always complete the test in the amount of time given.
- Use the test as an information tool. Be on the lookout for clues that answer other questions. Frequently, instructors will test you on a single topic in more than one way.
- Rule 6: Write in the Margin. Before you begin the test, write key terms, formulas, names, dates, and other information in the margin so you won’t forget them.
- Rule 7: Complete the Easy Questions First. Answering easy questions first helps build your confidence. If you come across a tough question, mark it so you can come back to it later. Avoid spending so much time on a challenging question that you might run out of time to answer the questions you do know.
- Rule 8: Know If There Is a Guessing Penalty. Chances are your tests will carry no penalty for guessing. If your time is about to run out and there is no penalty, take a wild guess. On the other hand, if your test carries a penalty for guessing, choose your answers wisely, and leave blank the answers you do not know.
- Rule 9: Avoid Changing Your Answers. Have you ever chosen an answer, changed it, and learned later that your first choice was correct? Research indicates that three out of four times, your first choice is correct; therefore, you should avoid changing an answer unless you are absolutely sure the answer is wrong.
- Rule 10: Write Clearly and Neatly. If you are handwriting your test (versus using a computer), imagine your instructor reading your writing. Is it easy to read or difficult? The easier your test is for the instructor to read, the better your chances of getting a higher grade.
Here are some websites to help you learn more about taking tests:
-
Essay tests and a checklist for essay tests
- www.calpoly.edu/~sas/asc/ael/tests.essay.html
-
Checklist for essay tests
- www.mtsu.edu/~studskl/essay.html
-
General test taking
- www.calpoly.edu/~sas/asc/ael/...s.general.html
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Post-test analysis
- www.calpoly.edu/~sas/asc/ael/....analysis.html


2.6.2: Free Energy Changes in Chemical Reactions
- Recall the possible free energy changes for chemical reactions.
The Direction and Extent of Chemical Change
ΔG determines the direction and extent of chemical change. Remember that ΔG is meaningful only for changes in which the temperature and pressure remain constant. These are the conditions under which most reactions are carried out in the laboratory. The system is usually open to the atmosphere (constant pressure) and the process is started and ended at room temperature (after any heat that has been added or which was liberated by the reaction has dissipated.)
The importance of the Gibbs function can hardly be over-stated: it determines whether a given chemical change is thermodynamically possible. Thus, if the free energy of the reactants is greater than that of the products, the entropy of the world will increase and the reaction takes place spontaneously. Conversely, if the free energy of the products exceeds that of the reactants, the reaction will not take place.
In a spontaneous change, Gibbs energy always decreases and never increases. This of course reflects the fact that the entropy of the world behaves in the exact opposite way (owing to the negative sign in the TΔS term). Here is an example:
H2O(liquid)→H2O(ice)H2O(liquid)→H2O(ice)
Water below zero degrees Celsius undergoes a decrease in its entropy, but the heat released into the surroundings more than compensates for this so the entropy of the world increases, the free energy of the H 2 O diminishes, and the process proceeds spontaneously.
An important consequence of the one-way downward path of the free energy is that once it reaches its minimum possible value, net change comes to a halt. This, of course, represents the state of chemical equilibrium. These relations are summarized as follows:
- ΔG<0ΔG<0: The reaction will occur spontaneously to the right.
- ΔG>0ΔG>0: The reaction will occur spontaneously to the left.
- ΔG=0ΔG=0: The reaction is at equilibrium and will not proceed in either direction.
Conditions for Spontaneous Change
Recall the condition for spontaneous change:
ΔG = ΔH – TΔS < 0
where ΔG = change in Gibbs free energy, ΔH = change in enthalpy, T = absolute temperature, and ΔS = change in entropy
It is apparent that the temperature dependence of ΔG depends almost entirely on the entropy change associated with the process. (it is appropriate to say “almost” because the values of ΔH and ΔS are themselves slightly temperature dependent; both gradually increase with temperature). In particular, notice that in the above equation the sign of the entropy change determines whether the reaction becomes more or less spontaneous as the temperature is raised.
For any given reaction, the sign of ΔH can also be positive or negative. This means that there are four possibilities for the influence that temperature can have on the spontaneity of a process:
Case 1: ΔH < 0 and ΔS > 0
Under these conditions, both the ΔH and TΔS terms will be negative, so ΔG will be negative regardless of the temperature. An exothermic reaction whose entropy increases will be spontaneous at all temperatures.
Case 2: ΔH < 0 and ΔS < 0
If the reaction is sufficiently exothermic it can force ΔG to be negative only at temperatures below which |TΔS| < |ΔH|. This means that there is a temperature defined by T=ΔHΔST=ΔHΔS at which the reaction is at equilibrium; the reaction will only proceed spontaneously below this temperature. The freezing of a liquid or the condensation of a gas are the most common examples of this condition.
Case 3: ΔH > 0 and ΔS > 0
This is the reverse of the previous case; the entropy increase must overcome the handicap of an endothermic process so that TΔS > ΔH. Since the effect of the temperature is to “magnify” the influence of a positive ΔS, the process will be spontaneous at temperatures above T=ΔHΔST=ΔHΔS. (Think of melting and boiling. )
Case 4: ΔH > 0 and ΔS < 0
With both ΔH and ΔS working against it, this kind of process will not proceed spontaneously at any temperature. Substance A always has a greater number of accessible energy states, and is therefore always the preferred form.
Key Points
- If the free energy of the reactants is greater than that of the products, the entropy of the world will increase when the reaction takes place as written, and so the reaction will tend to take place spontaneously.
- If the free energy of the products exceeds that of the reactants, then the reaction will not take place.
- An important consequence of the one-way downward path of the free energy is that once it reaches its minimum possible value, net change comes to a halt.
- In a spontaneous change, Gibbs energy always decreases and never increases.
Key Terms
- spontaneous change : A spontaneous process is the time-evolution of a system in which it releases free energy (usually as heat) and moves to a lower, more thermodynamically stable energy state.


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4: Social and Emotional Development in Infants and Toddlers (Birth to Age 3)
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4.0: What Does Psychology Say?
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The page describes the challenges and anxieties faced by new parents, Sarah and Amelia, as they care for their fussy eight-week-old baby, Asher. Amidst sleep deprivation, they experience conflicting advice from family and sources regarding childcare practices, such as whether picking up a crying baby spoils them, gender preferences in toys, the impact of screen time on infants, and the choice between daycare and home care. The chapter aims to address these concerns with current research.
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4.1: Autonomy and Sense of Self in Infants and Toddlers
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This section discusses early childhood development focused on autonomy, self-awareness, and gender identity. It explores how infants like Elyse begin to show independence and recognize themselves as separate beings from others. It highlights the mirror test as a measure of self-recognition. The text also delves into how gender identity starts forming early, influenced by cultural and societal gender stereotypes through interactions, toys, and media.
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4.2: Temperament and Personality in Infants and Toddlers
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This section covers the distinction between temperament and personality, highlighting different models of temperament and their characteristics. It discusses the environmental influences on temperament and the role of parenting in shaping a child's development. The theories of Thomas and Chess categorize infant temperament into easy, difficult, and slow-to-warm-up types, while Rothbart introduces surgency, negative affectivity, and effortful control.
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4.3: Emotional Development in Infants and Toddlers
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This section explores the development of emotions in early childhood, highlighting the relationship between emotions, mood, and emotion regulation. It differentiates between primary emotions, which are inherent and expressible through universal facial expressions like joy and sadness, and secondary emotions, which involve a sense of self, such as pride and jealousy.
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4.4: Social Development in Infants and Toddlers
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This section provides a comprehensive overview of social development in infancy and toddlerhood, focusing on attachment theory and styles, as well as cultural variations in attachment. It outlines key milestones such as social smiles, imitation, joint attention, and social referencing, which facilitate emotional and cognitive growth. The development of attachment styles, including secure, avoidant, ambivalent, and disorganized, is discussed alongside influential research by Bowlby and Ainsworth.
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4.5: Social Contexts and Influences in Infants and Toddlers
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This section discusses the contexts and variations in social and emotional development in infancy and toddlerhood, focusing on family and community influences. It highlights diverse family structures, child-rearing practices, and caregiving scenarios, including socio-economic and cultural factors.


1.1: Activity Last updated Save as PDF Page ID 375311 Michael J Blandamer & Joao Carlos R Reis University of Leicester & Faculdade de Ciencias 1.1.1: Acid Dissociation Constants- Weak Acids- Debye-Huckel Limiting Law 1.1.2: Acquisitive Convention 1.1.3: Activity- Solutions and Liquid Mixtures 1.1.4: Activity of Aqueous Solutions 1.1.5: Activity of Solvents 1.1.6: Activity of Solvents- Classic Analysis 1.1.7: Activity of Water - Foods 1.1.8: Activity of Water - One Solute 1.1.9: Activity of Water - Two Solutes 1.1.10: Activity Coefficient- Two Neutral Solutes- Solute + Trace Solute i 1.1.11: Activity Coefficients 1.1.12: Activity Coefficients- Salt Solutions- Ion-Ion Interactions 1.1.13: Activity of Water - Salt Solutions


7.7: Implications
What are the implications of a social constructionist approach to understanding the world? Because social constructionist analyses examine categories of difference as fluid, dynamic, and changing according to historical and geographical context, a social constructionist perspective suggests that existing inequalities are neither inevitable nor immutable. This perspective is especially useful for the activist and emancipatory aims of feminist movements and theories. By centering the processes through which inequality and power relations produce racialized, sexualized, and gendered differences, social constructionist analyses challenge the pathologization of minorities who have been thought to be essentially and inherently inferior to privileged groups. Additionally, social constructionist analyses destabilize the categories that organize people into hierarchically ordered groups through uncovering the historical, cultural, and/or institutional origins of the groups under study. In this way, social constructionist analyses challenge the categorical underpinnings of inequalities by revealing their production and reproduction through unequal systems of knowledge and power (Kang, et al., 2017).
As discussed in the section on social construction, heterosexuality is no more and no less “natural” than homosexuality or bisexuality. People—particularly sexologists and medical doctors—defined heterosexuality and its boundaries thus constructing an understanding we take for granted as real. This definition of the parameters of heterosexuality is an expression of power that constructs what types of sexuality are considered “normal” and which types of sexuality are considered “deviant.” Situated cultural norms define what is considered “natural.”  However, even within sexual relations between men and women, gendered cultural norms associated with heterosexuality dictate what is “normal” or “deviant.” As a quick thought exercise, think of some words for women who have many sexual partners, and then, do the same for men who have many sexual partners; the results will be quite different. So, within the field of sexuality we can see power in relations along lines of gender and sexual orientation (not to mention race, class, age, and ability).
 Compulsory heterosexuality plays an important role in reproducing inequality in the lives of sexual minorities. Just look at laws; in a few states, such as Indiana, joint adoptions are illegal for gay men and lesbians (Lambda Legal). Gay men and lesbians have lost custody battles over children due to homophobia —the fear, hatred, or prejudice against gay people (Pershing, 1994). Media depictions of gay men and lesbians are few and often negatively stereotyped. There are few “out” gay athletes in the top three men’s professional sports—basketball, baseball, and football—despite the fact that, statistically, there are very likely to be many (Zirin, 2010). Many religious groups openly exclude and discriminate against gay men and lesbians. Additionally, heteronormativity structures the everyday, taken-for-granted ways in which heterosexuality is privileged and normalized. For instance, sociologist Karen Martin studied what parents say to their children about sexuality and reproduction, and found that with children as young as three and five years old, parents routinely assumed their children were heterosexual, told them they would get (heterosexually) married, and interpreted cross-gender interactions between children as “signs” of heterosexuality (Martin 2009). In this kind of socialization is an additional element of normative sexuality—the idea of compulsory monogamy , where exclusive romantic and sexual relationships and marriage are expected and valued over other kinds of relationships (Willey 2016). Therefore, heteronormativity surrounds us at a very young age, teaching us that there are only two genders, and that we should desire and partner with one person of the opposite gender, who we will marry.
Just like gender, sexuality is neither binary nor fixed.   As there are more than two genders, there are more than two kinds of people to be attracted to, and individuals can be attracted to and can relate sexually to multiple people of different genders at once!
Another common misconception is that all transgender people are sexually queer. This belief may stem from the “LGBT” acronym that lists transgender people along with lesbians, gay men, and bisexuals. A trans man who previously identified as a lesbian may still be attracted to women and may identify as straight, or may identify as queer. Another trans man may be attracted to other men and identify as gay or queer. This multiplicity suggests that the culturally dominant binary model fails to accurately encapsulate the wide variety of sexual and gender lived experiences (Kang, et al., 2017).
No two people are the same, and it is important to view sexuality as a spectrum, in order to eliminate the potential for biases or generalizations.
For my entire childhood, I felt as if I could only be gay or straight and nothing in between. It wasn’t until I was in my early twenties that I realized that I was genuinely attracted to more than one gender. I spent a great amount of time worrying about the way people perceived me, until I began understanding the spectrum of sexuality. I’ve also received a lot of criticism from people around me regarding the idea of bisexuality and monogamy. I prefer monogamy over polyamory, and the people close to me know this, however; many people continue to believe that monogamy and bisexuality cannot work together. While I believe bisexuality and monogamy can coexist, I’ve had to begin the process of unlearning the stereotypes associated with sexuality and learn to disregard the generalizations put forth by other people.
 It's important to understand and embrace your sexuality as you feel without regard to the opinions of other people!


10.2: The χ2 test of independence (or association)
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| GUARDBOT1: | Halt! |
| GUARDBOT2: | Be you robot or human? |
| LEELA: | Robot…we be. |
| FRY: | Uh, yup! Just two robots out roboting it up! Eh? |
| GUARDBOT1: | Administer the test. |
| GUARDBOT2: | Which of the following would you most prefer? A: A puppy, B: A pretty flower from your sweetie, or C: A large properly-formatted data file? |
| GUARDBOT1: | Choose! |
– Futurama, “Fear of a Bot Planet
The other day I was watching an animated documentary examining the quaint customs of the natives of the planet
Chapek 9
. Apparently, in order to gain access to their capital city, a visitor must prove that they’re a robot, not a human. In order to determine whether or not visitor is human, they ask whether the visitor prefers puppies, flowers or large, properly formatted data files. “Pretty clever,” I thought to myself “but what if humans and robots have the same preferences? That probably wouldn’t be a very good test then, would it?” As it happens, I got my hands on the testing data that the civil authorities of
Chapek 9
used to check this.  I saved their data in a file called
chapek9.Rdata
, which I can now load and have a quick look at:
load( "./rbook-master/data/chapek9.Rdata" )
str(chapek9)
## 'data.frame': 180 obs. of 2 variables:
## $ species: Factor w/ 2 levels "robot","human": 1 2 2 2 1 2 2 1 2 1 ...
## $ choice : Factor w/ 3 levels "puppy","flower",..: 2 3 3 3 3 2 3 3 1 2 ...
Okay, so we have a single data frame called
chapek9
, which contains two factors,
species
and
choice
. As always, it’s nice to have a quick look at the data,
head(chapek9)
## species choice
## 1 robot flower
## 2 human data
## 3 human data
## 4 human data
## 5 robot data
## 6 human flower
and then take a
summary()
,
summary(chapek9)
## species choice
## robot:87 puppy : 28
## human:93 flower: 43
## data :109
In total there are 180 entries in the data frame, one for each person (counting both robots and humans as “people”) who was asked to make a choice. Specifically, there’s 93 humans and 87 robots; and overwhelmingly the preferred choice is the data file. However, these summaries don’t address the question we’re interested in. To do that, we need a more detailed description of the data. What we want to do is look at the
choices
broken down
by
species
. That is, we need to cross-tabulate the data (see Section 7.1). There’s quite a few ways to do this, as we’ve seen, but since our data are stored in a data frame, it’s convenient to use the
xtabs()
function.
chapekFrequencies <- xtabs( ~ choice + species, data = chapek9)
chapekFrequencies
## species
## choice robot human
## puppy 13 15
## flower 30 13
## data 44 65
That’s more or less what we’re after. So, if we add the row and column totals (which is convenient for the purposes of explaining the statistical tests), we would have a table like this,
| Robot | Human | Total | |
|---|---|---|---|
| Puppy | 13 | 15 | 28 |
| Flower | 30 | 13 | 43 |
| Data file | 44 | 65 | 109 |
| Total | 87 | 93 | 180 |
| which actual | ly would | be a nice | way to report the descriptive statistics for this data set. In any case, it’s quite clear that the vast majority of the humans chose the data file, whereas the robots tended to be a lot more even in their preferences. Leaving aside the question of why the humans might be more likely to choose the data file for the moment (which does seem quite odd, admittedly), our first order of business is to determine if the discrepancy between human choices and robot choices in the data set is statistically significant. |
Constructing our hypothesis test
How do we analyse this data? Specifically, since my research hypothesis is that “humans and robots answer the question in different ways”, how can I construct a test of the null hypothesis that “humans and robots answer the question the same way”? As before, we begin by establishing some notation to describe the data:
| Robot | Human | Total | |
|---|---|---|---|
| Puppy | O 11 | O 12 | R 1 |
| Flower | O 21 | O 22 | R 2 |
| Data file | O 31 | O 32 | R 3 |
| Total | C 1 | C 2 | N |
In this notation we say that O ij is a count (observed frequency) of the number of respondents that are of species j (robots or human) who gave answer i (puppy, flower or data) when asked to make a choice. The total number of observations is written N, as usual. Finally, I’ve used R i to denote the row totals (e.g., R 1 is the total number of people who chose the flower), and C j to denote the column totals (e.g., C 1 is the total number of robots). 176
So now let’s think about what the null hypothesis says. If robots and humans are responding in the same way to the question, it means that the probability that “a robot says puppy” is the same as the probability that “a human says puppy”, and so on for the other two possibilities. So, if we use P ij to denote “the probability that a member of species j gives response i” then our null hypothesis is that:
| H0: | All of the following are true: |
| P 11 =P 12 (same probability of saying puppy) | |
| P 21 =P 22 (same probability of saying flower) and | |
| P 31 =P 32 (same probability of saying data). |
And actually, since the null hypothesis is claiming that the true choice probabilities don’t depend on the species of the person making the choice, we can let P i refer to this probability: e.g., P 1 is the true probability of choosing the puppy.
Next, in much the same way that we did with the goodness of fit test, what we need to do is calculate the expected frequencies. That is, for each of the observed counts O ij , we need to figure out what the null hypothesis would tell us to expect. Let’s denote this expected frequency by E ij . This time, it’s a little bit trickier. If there are a total of C j people that belong to species j, and the true probability of anyone (regardless of species) choosing option i is P i , then the expected frequency is just:
\(E_{i j}=C_{j} \times P_{i}\)
Now, this is all very well and good, but we have a problem. Unlike the situation we had with the goodness of fit test, the null hypothesis doesn’t actually specify a particular value for P i . It’s something we have to estimate (Chapter 10) from the data! Fortunately, this is pretty easy to do. If 28 out of 180 people selected the flowers, then a natural estimate for the probability of choosing flowers is 28/180, which is approximately .16. If we phrase this in mathematical terms, what we’re saying is that our estimate for the probability of choosing option i is just the row total divided by the total sample size:
\(\hat{P}_{i}=\dfrac{R_{i}}{N}\)
Therefore, our expected frequency can be written as the product (i.e. multiplication) of the row total and the column total, divided by the total number of observations: 177
\(E_{i j}=\dfrac{R_{i} \times C_{j}}{N}\)
Now that we’ve figured out how to calculate the expected frequencies, it’s straightforward to define a test statistic; following the exact same strategy that we used in the goodness of fit test. In fact, it’s pretty much the same statistic. For a contingency table with r rows and c columns, the equation that defines our X 2 statistic is
\(X^{2}=\sum_{i=1}^{r} \sum_{j=1}^{c} \dfrac{\left(E_{i j}-O_{i j}\right)^{2}}{E_{i j}}\)
The only difference is that I have to include two summation sign (i.e., ∑) to indicate that we’re summing over both rows and columns. As before, large values of X 2 indicate that the null hypothesis provides a poor description of the data, whereas small values of X 2 suggest that it does a good job of accounting for the data. Therefore, just like last time, we want to reject the null hypothesis if X 2 is too large.
Not surprisingly, this statistic is X 2 distributed. All we need to do is figure out how many degrees of freedom are involved, which actually isn’t too hard. As I mentioned before, you can (usually) think of the degrees of freedom as being equal to the number of data points that you’re analysing, minus the number of constraints. A contingency table with r rows and c columns contains a total of r×c observed frequencies, so that’s the total number of observations. What about the constraints? Here, it’s slightly trickier. The answer is always the same
df=(r−1)(c−1)
but the explanation for why the degrees of freedom takes this value is different depending on the experimental design. For the sake of argument, let’s suppose that we had honestly intended to survey exactly 87 robots and 93 humans (column totals fixed by the experimenter), but left the row totals free to vary (row totals are random variables). Let’s think about the constraints that apply here. Well, since we deliberately fixed the column totals by Act of Experimenter, we have c constraints right there. But, there’s actually more to it than that. Remember how our null hypothesis had some free parameters (i.e., we had to estimate the P i values)? Those matter too. I won’t explain why in this book, but every free parameter in the null hypothesis is rather like an additional constraint. So, how many of those are there? Well, since these probabilities have to sum to 1, there’s only r−1 of these. So our total degrees of freedom is:
df=(number of observations)−(number of constraints)
=(rc)−(c+(r−1))
=rc−c−r+1
=(r−1)(c−1)
Alternatively, suppose that the only thing that the experimenter fixed was the total sample size N. That is, we quizzed the first 180 people that we saw, and it just turned out that 87 were robots and 93 were humans. This time around our reasoning would be slightly different, but would still lead is to the same answer. Our null hypothesis still has r−1 free parameters corresponding to the choice probabilities, but it now also has c−1 free parameters corresponding to the species probabilities, because we’d also have to estimate the probability that a randomly sampled person turns out to be a robot. 178 Finally, since we did actually fix the total number of observations N, that’s one more constraint. So now we have, rc observations, and (c−1)+(r−1)+1 constraints. What does that give?
df=(number of observations)−(number of constraints)
=rc−((c−1)+(r−1)+1)
=rc−c−r+1
=(r−1)(c−1)
Amazing.
Doing the test in R
Okay, now that we know how the test works, let’s have a look at how it’s done in R. As tempting as it is to lead you through the tedious calculations so that you’re forced to learn it the long way, I figure there’s no point. I already showed you how to do it the long way for the goodness of fit test in the last section, and since the test of independence isn’t conceptually any different, you won’t learn anything new by doing it the long way. So instead, I’ll go straight to showing you the easy way. As always, R lets you do it multiple ways. There’s the
chisq.test()
function, which I’ll talk about in Section @ref(chisq.test, but first I want to use the
associationTest()
function in the
lsr
package, which I think is easier on beginners. It works in the exact same way as the
xtabs()
function. Recall that, in order to produce the contingency table, we used this command:
xtabs( formula = ~choice+species, data = chapek9 )
## species
## choice robot human
## puppy 13 15
## flower 30 13
## data 44 65
The
associationTest()
function has exactly the same structure: it needs a
formula
that specifies which variables you’re cross-tabulating, and the name of a
data
frame that contains those variables. So the command is just this:
associationTest( formula = ~choice+species, data = chapek9 )
##
## Chi-square test of categorical association
##
## Variables: choice, species
##
## Hypotheses:
## null: variables are independent of one another
## alternative: some contingency exists between variables
##
## Observed contingency table:
## species
## choice robot human
## puppy 13 15
## flower 30 13
## data 44 65
##
## Expected contingency table under the null hypothesis:
## species
## choice robot human
## puppy 13.5 14.5
## flower 20.8 22.2
## data 52.7 56.3
##
## Test results:
## X-squared statistic: 10.722
## degrees of freedom: 2
## p-value: 0.005
##
## Other information:
## estimated effect size (Cramer's v): 0.244
Just like we did with the goodness of fit test, I’ll go through it line by line. The first two lines are, once again, just reminding you what kind of test you ran and what variables were used:
Chi-square test of categorical association
Variables: choice, species
Next, it tells you what the null and alternative hypotheses are (and again, I want to remind you not to get used to seeing these hypotheses written out so explicitly):
Hypotheses:
null: variables are independent of one another
alternative: some contingency exists between variables
Next, it shows you the observed contingency table that is being tested:
Observed contingency table:
species
choice robot human
puppy 13 15
flower 30 13
data 44 65
and it also shows you what the expected frequencies would be if the null hypothesis were true:
Expected contingency table under the null hypothesis:
species
choice robot human
puppy 13.5 14.5
flower 20.8 22.2
data 52.7 56.3
The next part describes the results of the hypothesis test itself:
Test results:
X-squared statistic: 10.722
degrees of freedom: 2
p-value: 0.005
And finally, it reports a measure of effect size:
Other information:
estimated effect size (Cramer's v): 0.244
You can ignore this bit for now. I’ll talk about it in just a moment.
This output gives us enough information to write up the result:
Pearson’s χ2 revealed a significant association between species and choice (χ 2 (2)=10.7,p<.01): robots appeared to be more likely to say that they prefer flowers, but the humans were more likely to say they prefer data.
Notice that, once again, I provided a little bit of interpretation to help the human reader understand what’s going on with the data. Later on in my discussion section, I’d provide a bit more context. To illustrate the difference, here’s what I’d probably say later on:
The fact that humans appeared to have a stronger preference for raw data files than robots is somewhat counterintuitive. However, in context it makes some sense: the civil authority on Chapek 9 has an unfortunate tendency to kill and dissect humans when they are identified. As such it seems most likely that the human participants did not respond honestly to the question, so as to avoid potentially undesirable consequences. This should be considered to be a substantial methodological weakness.
This could be classified as a rather extreme example of a reactivity effect, I suppose. Obviously, in this case the problem is severe enough that the study is more or less worthless as a tool for understanding the difference preferences among humans and robots. However, I hope this illustrates the difference between getting a statistically significant result (our null hypothesis is rejected in favour of the alternative), and finding something of scientific value (the data tell us nothing of interest about our research hypothesis due to a big methodological flaw).
Postscript
I later found out the data were made up, and I’d been watching cartoons instead of doing work.


<IP_ADDRESS>.1: Obtain Protection
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Obtaining Patent Protection
Unlike copyright, a patent is not automatically granted when someone has an interesting idea and writes it down. In most countries, a patent application must be submitted to a government patent office. A patent will only be granted if the invention or process being submitted meets certain conditions:
- It must be original. The invention being submitted must not have been submitted before.
- It must be non-obvious. You cannot patent something that anyone could think of. For example, you could not put a pencil on a chair and try to get a patent for a pencil-holding chair.
- It must be useful. The invention being submitted must serve some purpose or have some use that would be desired.
The job of the patent office is to review patent applications to ensure that the item being submitted meets these requirements. This is not an easy job: in 2012, the US Patent Office received 576,763 patent applications and granted 276,788 patents. The current backlog for a patent approval is 18.1 months. Over the past fifty years, the number of patent applications has risen from just 100,000 a year to almost 600,000; digital technologies are driving much of this innovation.
Sidebar: What Is a Patent Troll?
The advent of digital technologies has led to a large increase in patent filings and therefore a large number of patents being granted. Once a patent is granted, it is up to the owner of the patent to enforce it; if someone is found to be using the invention without permission, the patent holder has the right to sue to force that person to stop and to collect damages.
The rise in patents has led to a new form of profiteering called patent trolling. A patent troll is a person or organization who gains the rights to a patent but does not actually make the invention that the patent protects. Instead, the patent troll searches for those who are illegally using the invention in some way and sues them. In many cases, the infringement being alleged is questionable at best. For example, companies have been sued for using Wi-Fi or for scanning documents , technologies that have been on the market for many years.
Recently, the US government has begun taking action against patent trolls. Several pieces of legislation are working their way through Congress that will, if enacted, limit the ability of patent trolls to threaten innovation. You can learn a lot more about patent trolls by listening to a detailed investigation conducted by the radio program This American Life, by clicking this link.


3.4: The Nucleus and DNA Replication
The nucleus is the largest and most prominent of a cell’s organelles (Figure 3.19). The nucleus is generally considered the control center of the cell because it stores all of the genetic instructions for manufacturing proteins. Interestingly, some cells in the body, such as muscle cells, contain more than one nucleus (Figure 3.20), which is known as multinucleated. Other cells, such as mammalian red blood cells (RBCs), do not contain nuclei at all. RBCs eject their nuclei as they mature, making space for the large numbers of hemoglobin molecules that carry oxygen throughout the body (Figure 3.21). Without nuclei, the life span of RBCs is short, and so the body must produce new ones constantly.
Inside the nucleus lies the blueprint that dictates everything a cell will do and all of the products it will make. This information is stored within DNA. The nucleus sends “commands” to the cell via molecular messengers that translate the information from DNA. Each cell in your body (with the exception of germ cells) contains the complete set of your DNA. When a cell divides, the DNA must be duplicated so that the each new cell receives a full complement of DNA. The following section will explore the structure of the nucleus and its contents, as well as the process of DNA replication.
Organization of the Nucleus and Its DNA
Like most other cellular organelles, the nucleus is surrounded by a membrane called the nuclear envelope . This membranous covering consists of two adjacent lipid bilayers with a thin fluid space in between them. Spanning these two bilayers are nuclear pores. A nuclear pore is a tiny passageway for the passage of proteins, RNA, and solutes between the nucleus and the cytoplasm. Proteins called pore complexes lining the nuclear pores regulate the passage of materials into and out of the nucleus. Inside the nuclear envelope is a gel-like nucleoplasm with solutes that include the building blocks of nucleic acids. There also can be a dark-staining mass often visible under a simple light microscope, called a nucleolus (plural = nucleoli). The nucleolus is a region of the nucleus that is responsible for manufacturing the RNA necessary for construction of ribosomes. Once synthesized, newly made ribosomal subunits exit the cell’s nucleus through the nuclear pores. The genetic instructions that are used to build and maintain an organism are arranged in an orderly manner in strands of DNA. Within the nucleus are threads of chromatin composed of DNA and associated proteins (Figure 3.22). Along the chromatin threads, the DNA is wrapped around a set of histone proteins. A nucleosome is a single, wrapped DNA-histone complex. Multiple nucleosomes along the entire molecule of DNA appear like a beaded necklace, in which the string is the DNA and the beads are the associated histones. When a cell is in the process of division, the chromatin condenses into chromosomes, so that the DNA can be safely transported to the “daughter cells.” The chromosome is composed of DNA and proteins; it is the condensed form of chromatin. It is estimated that humans have almost 22,000 genes distributed on 46 chromosomes.
Contributors and Attributions
- Chapter 3. Authored by : OpenStax College. Provided by : Rice University. Located at : http://cnx.org/contents/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22<EMAIL_ADDRESS>. Project : Anatomy & Physiology. License : CC BY: Attribution . License Terms : Download for free at http://cnx.org/content/col11496/latest/ .