Washout with a one-week half-life: the arithmetic — does this still hold? posts 31–46

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.

I am reporting what happened, not recommending it.

Small correction to my own earlier position on Washout. I had the units the wrong way round, which changes the conclusion by an order of magnitude and therefore changes it entirely.

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.

Taking post #31 at face value and following it one step further.

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.

Adding the boring version of Washout, because the interesting version keeps getting posted and the boring one is usually right.

Check the ordinary explanations, in order, and stop when one of them accounts for what you are seeing. Most of the time the second one does.

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

That matches what I was told, which is not the same as knowing it.

Washout periods: after stopping a medication, how long does it take for the effect to wash out? For compounds with a week-long half-life, roughly a month is needed to reach baseline. Using that washout period in a before-after design strengthens the inference.

The variance between people here is larger than the effect being discussed.

That is a cleaner way of putting what I was circling around.

Helpful, and easy to find again, which is half of what a good reply is.

What I would want before treating Washout as settled: the method, the sample, and whether anyone tried to find the opposite result. Two of the three are usually missing.

Post #40 is right about the mechanism and I think understates the practical bit.

Washout is well covered in the tag pages, and the older discussions are better than the recent ones because they were argued out properly. Worth twenty minutes before adding to this one.

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.

This is the sort of thing that ought to be settled and apparently is not.

Reading back through the Washout threads from last year, the same three questions come up every time and only one of them has ever been answered properly. That seems like a documentation gap rather than a knowledge gap.

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.