Topic summary

Random versus fixed effects: choosing rather than defaulting

Evidence › Meta-analyses effect size publication bias risk of bias heterogeneity meta-analysis Closed

This is a generated summary. It shows the 5 most-liked posts from a topic of 21, 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.

l.aaltonenTL3Regular14 Jun 2025#4

Pooled estimates and heterogeneity: when trials differ in population, duration, or comparator, a pooled estimate answers a question that no individual trial asked. High heterogeneity means effects genuinely differ across studies. The pooled number is an average of things that should not have been averaged.

23 likes 13mo

h.nwosuTL219 Jun 2025#7

Ostrowski, post #6: Taking post #3 at face value and following it one step further. Where the pooled result and the largest single trial disagree, that disagreement is the interesting thing rather than an inconvenience to be smoothed. I would want a second opinion before relying on that. Go to post

Everything in post #3 holds. The case it does not cover is the one I have.

Practical note on random versus fixed effects: write down what you expect before you look. The number of times I have found what I went looking for is higher than chance would allow.

33 likes in reply to #6 13mo

m.oyelaranTL227 Jun 2025#12

Fixed-effects versus random-effects models: fixed-effects assumes all studies are estimating the same thing and variation is sampling error. Random-effects assumes studies are estimating effects from different distributions and allows between-study variance. Choice matters if heterogeneity is high.

A single observation, in a thread that deserves better than single observations.

26 likes 13mo

bench_peakTL3Regular6 Jul 2025#19

Taking random versus fixed effects 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.

25 likes 13mo

system_suitabilityTL3Analytical chemist9 Jul 2025 · edited#21

Birkeland, post #13: The version of random versus fixed effects 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. Go to post

Worth separating two things that post #19 runs together.

An observation about random versus fixed effects that I cannot explain and am posting anyway, on the principle that unexplained observations are more useful public than private.

20 likes in reply to #13 13mo

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