Evidence-appraisal glossary
Optimal Information Size
The optimal information size is the number of participants or events a body of evidence would need to reliably detect a given effect, roughly the sample a single adequately powered trial would require. Falling short of it is a reason to rate evidence down for imprecision.
Also called: OIS, information size.
A meta-analysis can look impressive yet still rest on too few events to rule out chance, much as an underpowered single trial would. The optimal information size gives a benchmark: if the pooled total does not reach the number needed to detect a plausible effect, the estimate is fragile even when the confidence interval looks narrow. It reframes imprecision as a question of total information, reminding readers that pooling studies does not automatically confer adequate power.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.