Meta‐analysis of Nonrandomized Controlled Trials Is Rarely Justified: Systematic Reviews Must Avoid Improper Pooling

This is the authors' abstract. We don't add key points for this paper.

Systematic reviews of the literature, as compared with original scientific articles, are the easiest types of studies to perform, and using contemporary meta-analysis software, the press of a button yields a "pooled weighted mean" (averaging the outcomes of the included articles and adjusting for sample size). The results seem conclusive. However, if included studies are not homogeneous and/or are of lower quality (high risk of bias), which is typical of nonrandomized trials, synthesis in a meta-analysis is not recommended, and quantitative pooling of nonrandomized studies is improper. In addition, by exploring clinical and methodologic differences (heterogeneity) between studies included in a systematic review, we discover and reveal reasons for the differences in outcomes among studies. This allows us to more accurately inform individual patient care and future research.