Background This post is the first installment of a two-part series. The impetus is a project at work. A colleague had longitudinal data for participants in two experimental groups, which they examined with a multilevel growth model of the kind we’ll explore in the next post. My colleague then summarized the difference in growth for the two conditions with a standardized mean difference they called \(d\). Their effect size looked large, to me, and I was perplexed when I saw the formula they ...
