Washout with a one-week half-life: the arithmetic — does this still hold?

I disagree with the framing of Washout 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.

Post #10 answers the question as asked. The question underneath it is different.

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.

That is where I would start, not where I would stop.

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.

I had written a reply contradicting post #24 and deleted it. Here is what survived.

Reporting rather than recommending, on Washout. What happened is above. Whether it should have is a different question and not one I am qualified to answer.

Post #31 and I disagree about the size of the effect, not about the direction.

Where I have landed on Washout, having got it wrong once in public: the direction is clear, the magnitude is not, and anyone quoting a precise magnitude has borrowed it from somewhere that did not measure it.

On post #42 — agreed on the reasoning, with one qualification.

The reason Washout keeps being re-asked is that the answer is conditional and people quote it without the condition. It is not that the answer is unknown.