Most psychologists agree that a person's basic personality—whether they are an introvert or extrovert, for example—remains the same throughout life. What we might see as personality changes are actually just responses to external factors, such as getting a job, getting married or becoming a parent. That said, research does indicate that our personalities become more solidified, or stable, as we get older. 
 
 That change is not linear, however. New research indicates that our personalities become increasingly stable as our 20s melt into our 30s, 40s and even 50s, but that that stability then often begins to taper off in old age, Research Digest reports. 
 
 Researchers in New Zealand recruited 4,000 men and women aged 20 to 80 to complete a personality questionnaire twice, with a gap of two years in between. The survey measured a person's honesty-humility factor as well as five major personality traits: extraversion, agreeableness, conscientiousness, neuroticism and openness to experience, Research Digest writes. They compared how people's scores varied between years, and analyzed how all of the participants personalities related to one another, depending on age. 
 
 Most people's personalities were generally stable, they found, but the stability of those trait followed a bell curve over time, peaking at middle-age and then dropping again. For certain traits—conscientiousness, openness to experience, and honesty-humility—Research Digest writes, the oldest participants' personality stability matched those of the youngest. 
 
 Other interesting finds included "domain specific" variations, or ones that seem to be linked to what a person is dealing with at a particular point in their life. People in their 30s, for example, showed high levels of neuroticism, but by the time they reached their 50s that had tapered off and had been replaced by conscientiousness, openness and honesty-humility. ||||| Photo: Nat Fein/Getty Images 
 
 At any given moment, an estimated 108 million people in the United States are on a diet. But despite the fact that the U.S. weight-loss industry makes roughly $20 billion in revenue each year, people continue to fail for one reason or another. Part of the problem, new research suggests, is that our eating habits are influenced by deep-seated personality traits. Your neuroticism, in other words, could be partially responsible for your love of chocolate and cheese. 
 
 For the study, published in the journal Appetite, researchers at the Swiss Federal Institute of Technology sent three questionnaires — one on personality, one on eating habits, and one on food choices — to a random sample of addresses. After excluding subjects who skipped more than 10 percent of the questions, data from nearly a thousand participants (with an average age of 55 years old) was analyzed. 
 
 The personality questions were designed to measure what psychologists believe are the five basic dimensions of personality — openness, conscientiousness, extroversion, agreeableness, and neuroticism. The researchers were curious whether, and to what extent, high or low scores on these different traits would correlate with certain eating habits. 
 
 “We found that a person’s personality does, in fact, determine why he or she eats and what he or she eats,” said Carmen Keller, the study’s lead author. For one thing, “A lack of conscientiousness leads people to eat impulsively and to lose self-control in the face of tempting food situations with palatable and nicely smelling and tasting food,” she explained. In addition, “Neurotic people may eat too much high-caloric food to deal with their negative emotions.” 
 
 Extroversion, which, unlike neuroticism or a lack of conscientiousness tends to have mostly positive connotations in society, was also linked to potentially unhealthy eating habits. “A surprising result is that extroverted people eat more due to external reasons — such as a nice smell or the taste of food — and, in turn, they often consume more meat, sweet foods, savory foods, and sugar-sweetened drinks,” explained Keller. “It might be that the higher sociability of extroverted people results in having more meals with other people and, therefore, eating foods that are not healthy.” Indeed, a lot of past research has suggested that social components greatly influence both what people eat and how frequently they exercise, including studies showing that people-pleasers eat more, women mimic each other’s eating behaviors, and finding a walking group can help you become healthier. 
 
 Taken together, the results reported by Keller and her team suggest that certain personality characteristics can be seen as “risk factors” for an unhealthy lifestyle. “These findings add to a growing body of evidence showing the importance of the personality traits of neuroticism and conscientiousness for a variety of health-related behaviors, including a healthy diet,” said Tim Bogg, an assistant professor of psychology at Wayne State University, who has studied conscientiousness and health, but who wasn’t involved in this study. “The results show that part of the complicated puzzle of maintaining a healthy diet over the long term is related to our general tendencies for emotion regulation and self-control, not simply how good we are at counting calories or avoiding trans fats.” 
 
 In other words, there could be an underrated “know thyself” aspect to successful weight management — understanding how you respond to a stressful day at work, say, or to attending a party where there’s likely to be a lot of food. As Fiona Johnson, a research associate at University College London who also wasn’t affiliated with this study explained, since personality traits are “largely stable over the life course,” understanding the connection between them and eating habits could offer important new opportunities for people to better monitor and control their eating habits. “Overcoming these fundamental tendencies can be very difficult, and identifying ways in which people can boost their capacity to control their eating (eating self-regulation) is the next big challenge in eating research.” 
 
 There are limitations to this study — for example, it only sampled Swiss subjects, and did so with self-reported inventories — but it certainly adds some evidence to the common-sense notion that our personalities, which greatly influence how we react to just about everything, also affect what — and how much — to eat. So while there’s more research to be done, those trying to lose weight might want to look into not just calorie-counting apps and healthier foods at the supermarket, but personality inventories, too. ||||| EVANSTON, Ill. --- Northwestern University researchers have sifted through data from more than 1.5 million questionnaire respondents and found at least four distinct clusters of personality types exist: average, reserved, self-centered and role model. The findings challenge existing paradigms in psychology. 
 
 The new study, led by Luís Amaral of the McCormick School of Engineering, will be published Sept. 17 by the journal Nature Human Behaviour. The findings potentially could be of interest to hiring managers and mental health care providers. 
 
 "People have tried to classify personality types since Hippocrates' time, but previous scientific literature has found that to be nonsense," said co-author William Revelle, professor of psychology in the Weinberg College of Arts and Sciences. 
 
 "Now, these data show there are higher densities of certain personality types," said Revelle, who specializes in personality measurement, theory and research. 
 
 Initially, however, Revelle was skeptical of the study's premise. The concept of personality types remains controversial in psychology, with hard scientific proof difficult to find. Previous attempts based on small research groups created results that often were not replicable. 
 
 "Personality types only existed in self-help literature and did not have a place in scientific journals," said Amaral, the Erastus Otis Haven Professor of Chemical and Biological Engineering at Northwestern Engineering. "Now, we think this will change because of this study." 
 
 The new research combined an alternative computational approach with data from four questionnaires with more than 1.5 million respondents from around the world obtained from John Johnson's IPIP-NEO with 120 and 300 items, respectively, the myPersonality project and the BBC Big Personality Test datasets. The questionnaires, developed by the research community over the decades, have between 44 and 300 questions. People voluntarily take the online quizzes attracted by the opportunity to receive feedback about their own personality. These data are now being made available to other researchers for independent analyses. 
 
 "The thing that is really, really cool is that a study with a dataset this large would not have been possible before the web," Amaral said. "Previously, maybe researchers would recruit undergrads on campus, and maybe get a few hundred people. Now, we have all these online resources available, and now data is being shared." 
 
 From those robust datasets, the team plotted the five widely accepted basic personality traits: neuroticism, extraversion, openness, agreeableness and conscientiousness. 
 
 After developing new algorithms, four clusters emerged: 
 
 Average Average people are high in neuroticism and extraversion, while low in openness. "I would expect that the typical person would be in this cluster," said Martin Gerlach, a postdoctoral fellow in Amaral's lab and the paper's first author. Females are more likely than males to fall into the Average type. Reserved The Reserved type is emotionally stable, but not open or neurotic. They are not particularly extraverted but are somewhat agreeable and conscientious. Role Models Role Models score low in neuroticism and high in all the other traits. The likelihood that someone is a role model increases dramatically with age. "These are people who are dependable and open to new ideas," Amaral said. "These are good people to be in charge of things. In fact, life is easier if you have more dealings with role models." More women than men are likely to be role models. Self-Centered Self-Centered people score very high in extraversion and below average in openness, agreeableness and conscientiousness. "These are people you don't want to hang out with," Revelle said. There is a very dramatic decrease in the number of self-centered types as people age, both with women and men. 
 
 The group's first attempt to sort the data used traditional clustering algorithms, but that yielded inaccurate results, Amaral said. 
 
 "At first, they came to me with 16 personality types, and there's enough literature that I'm aware of that says that's ridiculous," Revelle said. "I believed there were no types at all." 
 
 He challenged Amaral and Gerlach to refine their data. 
 
 "Machine learning and data science are promising but can be seen as a little bit of a religion," Amaral said. "You still need to test your results. We developed a new method to guide people to solve the clustering problem to test the findings." 
 
 Their algorithm first searched for many clusters using traditional clustering methods, but then winnowed them down by imposing additional constraints. This procedure revealed the four groups they reported. 
 
 "The data came back, and they kept coming up with the same four clusters of higher density and at higher densities than you'd expect by chance, and you can show by replication that this is statistically unlikely," Revelle said. 
 
 "I like data, and I believe these results," he added. "The methodology is the main part of the paper's contribution to science." 
 
 To be sure the new clusters of types were accurate, the researchers used a notoriously self-centered group -- teenaged boys -- to validate their information. 
 
 "We know teen boys behave in self-centered ways," Amaral said. "If the data were correct and sifted for demographics, they would they turn out to be the biggest cluster of people." 
 
 Indeed, young males are overrepresented in the Self-Centered group, while females over 15 years old are vastly underrepresented. 
 
 Along with serving as a tool that can help mental health service providers assess for personality types with extreme traits, Amaral said the study's results could be helpful for hiring managers looking to insure a potential candidate is a good fit or for people who are dating and looking for an appropriate partner. 
 
 And good news for parents of teenagers everywhere: As people mature, their personality types often shift. For instance, older people tend to be less neurotic yet more conscientious and agreeable than those under 20 years old. 
 
 "When we look at large groups of people, it's clear there are trends, that some people may be changing some of these characteristics over time," Amaral said. "This could be a subject of future research." 
 
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 The research was funded by a gift from Mac and Leslie McQuown along with support from Department of Defense Army Research Office and the National Science Foundation.
– There's no doubt about it: The human body goes through major changes in youth and old age. And these biological and social changes may be the reasons behind what researchers are calling less stable personalities at those life stages. In fact, according to a study of almost 4,000 New Zealanders between the ages of 20 and 80, the stability of one's personality increases through youth and into middle age and peaks in our 50s, before we slide back into less stable versions of ourselves, reports Research Digest. As the Smithsonian puts it, "in some ways, our 80-year-old selves mirror our 20-year-old selves." Some traits peaked at different times; the most stable traits in one's 30s are extraversion and neuroticism, while in the late 40s and early 50s it is openness, honesty-humility, and conscientiousness. The only trait that showed "gradually reduced stability" throughout life was agreeableness; apparently we are simply less and less agreeable as we pack the years on. Still, one's most basic personality—introvert vs. extrovert, for example—tends to remain consistent throughout one's life, even if the stability of traits waxes and wanes, notes the Smithsonian. (Other researchers have even calculated the country's most extroverted city.)