> Yes, but later the article shows that "mean difference" is really mean difference divided by variance. I would say later the article shows examples of standa

> Yes, but later the article shows that "mean difference" is really mean difference divided by variance. I would say later the article shows examples of standardized effect size, so divides by variance. Whether that means effect size can't be a difference in means (and explains the wiki intro comment) I disagree with--see my Lakens comment for why. > If you care about units, you can talk about the expected value/difference, but that doesn't make that a meaningful effect size. What you need to do in those cases is to, at least, mention both the expected difference and the variance. This seems like it is begging the question. If you look at the definition and rationale for effect size, both in the wikipedia and in Lakens, a claim this strong is not there. For example, a CI over difference in means is one way to capture what a standardized effect size that uses a specific variance term might be doing (what Lakens describes as the second ES viewpoint: statistical significance, distinguishing between effect and power). In any event, thanks for discussing--it's been really helpful to think about and revisit this topic!