At the core of biology and other sciences lies a problem-solving approach called the scientific method. 1  Make an observation. 2  Ask a question. 3  Form a hypothesis, or testable explanation. 4  Make a prediction based on the hypothesis.  Test the prediction.
Xi. Xi is the 14th letter of the Greek alphabet. It is pronounced in Modern Greek, and generally or in English. In the system of Greek numerals, it has a value of 60. Xi was derived from the Phoenician letter samekh. Xi is not to be confused with the letter chi, which gave its form to the Latin letter X.
Perhaps the most logical beginning would be to say that what is normal is the simple average of the data from each of the 100 samples. where the xi represent the individual values from each of 100 years in the period of record, and the funny symbol is read as  the sum from i =1 to 100 of the xi.