Rapid reviews may produce different results to systematic reviews: a meta-epidemiological study.

OBJECTIVE: To simulate possible changes in systematic review results if rapid review methods were used.

STUDY DESIGN AND SETTING: We re-calculated meta-analyses for binary primary outcomes in Cochrane systematic reviews, simulating rapid review methods. We simulated: searching only PubMed; excluding older articles (5, 7, 10, 15, and 20 years prior to the search date); excluding smaller trials (<50, <100, and <200 participants); and using the largest trial only. We examined percentage changes in: pooled odds ratios (ORs) (classed as no important change [<5%], small [<20%] moderate [<30%], or large [≥30%]); statistical significance; and biases observed using rapid methods.

RESULTS: 2,512 systematic reviews (16,088 studies) were included. Rapid methods resulted in the loss of all data in 3.7-44.7% of meta-analyses. Searching only PubMed had the smallest risk of changed ORs: (19% [477/2,512] were small changes or greater; 10% [260/2,512] were moderate or greater). Changes in ORs varied substantially with each rapid review method; 8.4-21.3% were small, 1.9-8.8% were moderate, and 4.7-34.1% were large. Changes in statistical significance occurred in 6.5-38.6% of meta-analyses. Changes from significant to non-significant were most common (2.1-13.7% meta-analyses). We found no evidence of bias with any rapid review method.

CONCLUSION: Searching PubMed only might be considered where a ∼10% risk of the primary outcome OR changing by >20% could be tolerated. This could be the case in scoping reviews, resource limitation, or where syntheses are needed urgently. Other situations, such as clinical guidelines and regulatory decisions, favour more comprehensive systematic review methods.