In Reply Mr Syn and Mr Wee questioned the rationale for excluding studies from our meta-analysis1 based on numbers of participants. Of 1385 articles identified in the systematic search, no studies were excluded based on the number of participants enrolled. However, there are several reasons for excluding small studies. Small studies are often of poorer methodological quality and have a higher risk of bias,2 and including them can exaggerate treatment effects and lead to misleading conclusions.3 Furthermore, small studies have negligible contributions when 2 or more adequately powered studies are included in a meta-analysis.3 These factors may justify the exclusion of small and underpowered studies from meta-analyses in which adequately powered studies already exist.3
Zheng SL, Roddick AJ. Meta-analysis of Aspirin for Primary Prevention of Cardiovascular Events—Reply. JAMA. 2019;321(22):2244–2245. doi:10.1001/jama.2019.4017
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