This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
Practical answer on pre-registering a personal experiment, since the theoretical one is upthread: do the simplest check first, write down the result, and only then decide whether the complicated explanation is needed. It usually is not.
That reframing is the whole thing. The facts I already had.
Write down what you would accept as evidence that it did not work, before starting. That one sentence turns an anecdote into an experiment.
I would treat that as a working assumption and revisit it.
Agreed on pre-registering a personal experiment, with one qualification that I think matters. The reasoning holds for the case as described. Change the starting assumption and it does not, and the starting assumption is the part nobody states.
A methods point on pre-registering a personal experiment rather than a substantive one: if the comparison is not like for like, the difference you are measuring is the difference in method.
This follows post #34 rather than contradicting it.
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 would rather be precise about what I do not know than vague about what I do.
I came in to disagree and I am leaving without a disagreement.
Taking pre-registering a personal experiment seriously for a moment rather than deflecting: the honest position is that the community has observations and no controlled comparison, and those two things support very different sentences.
On post #37 — agreed on the reasoning, with one qualification.
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.
I have kept the units in throughout, for the obvious reason.
Appreciated. The plain phrasing does more work here than a longer post would.
Speaking only to pre-registering a personal experiment as I have actually seen it, rather than as it is usually described: the effect is real, it is smaller than the thread suggests, and the variance between people is larger than the effect.
Measure the same thing the same way at the same time of day. Most of the noise in personal data is measurement protocol rather than biology.
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.
Worth one more sentence than it usually gets.
This follows post #45 rather than contradicting it.
A request rather than an answer: could whoever has the primary source for pre-registering a personal experiment post it? I have seen the claim three times this month and each version had lost a qualifier.
Coming back to post #45, because the follow-up matters more than the original answer.
Duration should be set by how long an effect would take to appear rather than by patience. Stopping early is the commonest reason a personal experiment answers nothing.
It is one reading of the data and not the only reasonable one.
I disagree with the framing of pre-registering a personal experiment above, and I think it is a substantive disagreement rather than a terminological one. Setting out why, so it can be checked.
The reasoning depends on an assumption that is doing a lot of work and is never stated. If the assumption holds, the conclusion follows. I do not think it holds generally.
Where the pre-registering a personal experiment reasoning breaks down for me is the step from the group result to the individual case. That step is almost never argued for.
Nothing in a personal experiment is medical advice to anyone including yourself, and several people here have found that a prescriber will happily discuss a well-documented one.
Reading it again, the caveat matters more than the finding.
The arithmetic in post #48 is right; the assumption feeding it is the part to check.
Genuine question rather than a rhetorical one: has anyone here actually observed pre-registering a personal experiment, as opposed to read about it? The thread is long and I cannot tell.
Answering the question post #50 raises rather than the one it answers.
Designing a personal experiment that could actually change your mind: that is the standard for an n-of-1 design. An experiment designed so that any result confirms what you already believed has not changed anything.
Take it as a starting point and not as a specification.
The version of pre-registering a personal experiment that circulates here is a simplification of a simplification. It is not wrong, but it has lost the conditions under which it holds, and those conditions are where the interesting cases live.
Order effects matter. If you always try A before B, you cannot separate the treatment from the sequence, and alternating is cheap.
Adding the measurement that post #52 says would settle it.
Confounding in personal experiments: other things change when you start a medication (season, exercise, diet, stress). Documenting those confounders helps you understand their contribution to the result.
Worth saying I have only my own numbers here, and n is small.
Two people in this thread mean different things by pre-registering a personal experiment and are disagreeing about the definition while believing they are disagreeing about the facts. Worth pausing to define it.
What I can speak to on pre-registering a personal experiment is narrow, so I will keep it narrow rather than generalising from it. Beyond that boundary I do not know.
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.