think that all you have to do is a simple t test between the averages for males and females and then another simple t test for the averages between those who participated in the high-impact and those who participated in the low-impact treatment—and you would have found nothing. But, using the idea of an interaction between main factors, you find out that there is a differential effect—an outcome that would have gone unnoticed otherwise. Indeed, if you can bear the cost of admission, interactions really are the most interesting outcomes in any factorial analysis of variance. Consider including
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