Never Tell Me the Odds (Ratio)

https://slatestarcodex.com/2020/04/07/never-tell-me-the-odds-ratio/

[Epistemic status: low confidence, someone tell me if the math is off. Title was stolen from an old Less Wrong post that seems to have disappeared – let me know if it’s yours and I’ll give you credit]

I almost screwed up yesterday’s journal club. The study reported an odds ratio of 2.9 for antidepressants. Even though I knew odds ratios are terrible and you should never trust your intuitive impression of them, I still mentally filed this away as “sounds like a really big effect”.

This time I was saved by Chen’s How Big is a Big Odds Ratio? Interpreting the Magnitudes of Odds Ratios in Epidemiological Studies, which explains how to convert ORs into effect sizes. Colored highlights are mine. I have followed the usual statistical practice of interpreting effect sizes of 0.2 as “small”, of 0.5 as “moderate”, and 0.8 as “large”, but feeling guilty about it.