Topic summary

Immortal time bias in a claims-database study — one year on

Evidence › Study critique effect size risk of bias confounding Solved

This is a generated summary. It shows the 7 most-liked posts from a topic of 47, in their original order, with the accepted answer included where one exists. It is a reading aid and it will miss nuance — the full topic is the record.

VPoulsenTL3Regular28 Jun 2026#1

Posting this under the heading it deserves: Immortal time bias in a claims-database study — one year on Everything below is what sits behind that.

I would like to disagree carefully with the settled view on Immortal time bias, and I would like to be argued out of it if the disagreement is bad.

The disagreement is about one step, not about the conclusion. If the step holds I withdraw it entirely.

26 likes 30d

methods_draftTL2Member30 Jun 2026#2

Reporting bias within a paper — a result in a figure that is absent from the abstract — is checkable and is worth checking when the claim matters.

28 likes 28d

p.trevinoTL2 Solution2 Jul 2026#5

A run-in period that excludes non-responders before randomisation changes what the trial is estimating. It is legitimate design and it must be stated in any summary.

20 likes 26d

y.adeyemiTL25 Jul 2026#9

Worth stating the null on Immortal time bias before we explain it: the observation may be nothing. That possibility deserves a sentence and usually does not get one.

27 likes 22d

KTurkingtonTL3Regular8 Jul 2026#12

Bias towards the null and bias away from the null: different criticisms have different directions. Differential dropout might bias away from null; conservative statistical analysis might bias toward null.

That is my reading. Someone else read the same page differently and was reasonable.

26 likes 20d

j.rasmussenTL2Regular15 Jul 2026#25

Generalisability and validity are separate axes. A trial can be internally impeccable and still tell you nothing about the person asking.

31 likes 12d

j.petrovTL218 Jul 2026#30

m.marchetti, post #3: Second-hand on Immortal time bias, so weight it accordingly — someone whose method I trust told me this and I have not verified it myself. Go to post

Where I part company with post #27, and it is a narrow parting.

On Immortal time bias the community has more anecdote than the confidence in this thread implies, and I include my own contribution in that.

24 likes in reply to #3 10d

Read the full topic (47 posts)

This topic was referenced in

A well-designed study with a badly written abstract — does this still hold?Evidence › Study critique · 2 replies

Moved from Trials by hana.sato. Category placement is not obvious from outside and getting it wrong is expected. This topic will get better answers here. The move is recorded in the public log citing R7.

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