Coming back to: Why most self-reports here are not experiments, and that is fine

It does not tell you about anybody else, which is why aggregating these accounts does not produce evidence of the kind people want it to.

Post #14 and I disagree about the size of the effect, not about the direction.

Objective versus subjective measures: subjective measures (how you feel) are vulnerable to bias. Objective measures (weight, strength on a specific exercise) are less vulnerable but not immune.

I keep a log of this specifically because memory is unreliable about it.

Narrowing post #16, because the general version has more than one answer.

Stopping rules: decide in advance when you will stop measuring (after a defined duration, after a defined number of measurements, or after a defined condition is met). Not deciding in advance means stopping when the result satisfies you, which is bias.

One case, stated as one case.

Record everything that changed, not just the intervention. Personal experiments are confounded by life, and the confounders are only recoverable if they were written down.

Stating my assumptions rather than smuggling them in.

Adding the measurement that post #16 says would settle it.

Sample size in n-of-1: you are the sample. Repeated measurements (weekly weighings, daily mood scores) increase the power to detect a real effect even though n=1.

Noting that I have skin in this question and have tried to discount for it.

A photograph or a device reading is a harder record than a recollection, and where one is available it should be the record.

A weak preference rather than a position.

Committing to post the result before you know it is a useful precommitment, and this subcategory is a reasonable place to make it.

Thank you for the correction. I would rather find out here than later.

Multiple outcomes measured without a primary one means something will move. Nominate the primary in advance and report the rest as secondary.

Filing this under things that are true until someone shows me otherwise.

Generalisability: a robust n-of-1 result applies to you. It does not tell you much about whether the effect generalises to others similar to you, much less to people different from you.

I had written a reply contradicting post #23 and deleted it. Here is what survived.

Order effects matter. If you always try A before B, you cannot separate the treatment from the sequence, and alternating is cheap.

Flagging that the sources on this are thinner than the confidence in the thread suggests.

Confirming post #23 from a second method, which matters more than confirming it from a second person.

A rolling mean over several days is far more informative than any single reading for anything that varies day to day, which is nearly everything.

The number is defensible. The precision I gave it is not.

The interesting personal experiments are the ones where the answer was no. They are also the ones least likely to be written up.

An n of one tells you about one person, which is the person you are most interested in. That is the whole value and it is not nothing.

Coming back to post #27, because the follow-up matters more than the original answer.

Order effects matter. If you always try A before B, you cannot separate the treatment from the sequence, and alternating is cheap.

Noting that the question and the thing people usually mean by it are different.