Instructions: For most studies, statistical significance is defined as a "p" value less than 0.05 (p<0.05). When used to compare differences on some feature (such as height) between two groups (professional basketball players versus FIDE-ranked chess players), p < 0.05 means that you would, by chance, expect a height difference as big as what you observed to only occur less than 1-in-20 times (1/20 = 0.05) if there was no actual height difference. That is, if we assume the group means are equal (the null hypothesis), and we randomly grabbed a small group of people from each of these equal-mean-height groups, sometimes just by chance, we'll see a difference in the average height. But bigger-and-bigger differences are less-and-less likely