N-of-1: How to Test Something on Yourself Without Fooling Yourself

Summary

Population studies tell you what works *on average*; they can't tell you whether a given thing works for **you** — that's an **n-of-1** question, and you can answer it honestly with a few cheap rules (define one outcome, change one thing at a time, use washouts and ideally blinding, run several on/off cycles, and beware regression to the mean and placebo) instead of the usual "I tried it and felt better" self-deception.