I did mention the following at the end of the "antidepressants" section, but reading your comment convinced me to move it further up. The intro now reads:
> The "standardised effect size" of antidepressants on depression, vs placebo, is around 0.4. (On average; some people respond much better or much worse.)
Also, I wasn't expecting my article to do well on Hacker News; thank you everyone for the comments & critiques! I'll edit the blog post as I go along, to refine it in response to your comments.