Evidence · Trials

Run-in periods and the population they select — the long version

Evidence › Trials randomised trial estimand intention to treat surrogate endpoints

a.lindqvistTL217 Oct 2025#1

Run-in periods and the population they select — the long version Writing it up because I had to work it out twice and would rather nobody else did.

A narrow question about Run-in periods, deliberately narrow, because the broad version has been asked here four times and produced four long threads and no answer.

One question, stated units, stated method, and what I have already ruled out.

55 likes 9mo

figure_reviewTL2Member18 Jan 2026#2

Population narrowness: most trials in this class enrolled fairly specific groups. Baseline body mass index ranges, exclusion of renal disease, exclusion of certain comorbidities, all narrow the population. Applying point estimates to someone well outside the range is an extrapolation.

I would rather post the uncertainty than round it away.

15 likes 6mo

e.kuipersTL225 Mar 2026#3

Where I part company with the opening post, and it is a narrow parting.

Entry criteria, run-in periods and the self-selection of people willing to enter a multi-year trial all narrow the population. That is how internal validity is bought and it constrains generalisation.

3 likes 4mo

Promoted into the documentation commons. The content of this topic is maintained at STEP 3 — trial digest, with named maintainers and a review date. The promotion was discussed in doc review. Corrections are best raised against the document, which is the version that gets kept current.

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