Next chapter: Chi Square

Consider the following situation in which luck alone determines performance: A coin is flipped 100 times and each student in a class asked to predict the outcome of each flip. The student who did the best in the class was right 62 times out of 100. The test is now given for a second time. What is the best prediction for the number of times this student will predict correctly? Since this test is all luck, the best prediction for any given student, including this one, is 50 correct guesses. Therefore, the prediction is that the score of 62 would regress all the way to the mean of 50. To take the other extreme, if a test were entirely skill and involved no luck at all, then there would be no regression toward the mean.

Next chapter: Chi Square