Evidence-appraisal glossary
Fixed-effect model
A fixed-effect meta-analysis assumes every included study is estimating one single true effect and combines them by weighting each study mainly by its size. It treats all differences between study results as chance alone.
Also called: common-effect model, fixed effect model.
It is appropriate when the studies are similar enough that a single common effect is plausible; it gives large studies more weight and produces narrower confidence intervals than a random-effects model. A frequent misreading is confusing the fixed-effect model (one true effect) with the unrelated regression idea of fixed effects, and if real between-study differences exist this model understates the true uncertainty.
Read the full Reading the Evidence blog.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.