Background Systematic reviews are often characterised as being inherently replicable but several studies have challenged this claim.

Objectives To investigate the variation in results following independent replication of literature searches and meta-analyses of systematic reviews.

Methods We included ten systematic reviews of the effects of health interventions published in November 2020. Two information specialists repeated the original database search strategies. Two experienced review authors screened full-text articles, extracted data, and calculated the results for the first reported meta-analysis. All replicators were initially blinded to the results of the original review. A meta-analysis was considered not ‘fully replicable’ if the original and replicated summary estimate or confidence interval width differed by more than 10%, and meaningfully different if there was a difference in the direction or statistical significance.

Results The difference between the number of records retrieved by the original reviewers and the information specialists exceeded 10% in 25/43 (58%) searches for the first replicator and 21/43 (49%) searches for the second. Eight meta-analyses (80%, 95% CI: 49-96%) were initially classified as not fully replicable. After screening and data discrepancies were addressed, the number of meta-analyses classified as not fully replicable decreased to five (50%, 95% CI: 24-76%). Differences were classified as meaningful in one blinded replication (10%, 95% CI: 1-40%) and none of the unblinded replications (0%, 95% CI: 0-28%).

Conclusions The results of systematic review processes were not always consistent when their reported methods were repeated. However, these inconsistencies seldom affected summary estimates from meta-analyses in a meaningful way.

What is already known on this topic

Systematic reviews are often characterised as being inherently replicable, however, several studies have challenged this claim.

Few studies have examined where and why inconsistencies arise, and what their impact is, when replicating multiple systematic review processes.

What this study adds

Replication of published systematic review processes (database searches, full-text screening, data extraction and meta-analysis) frequently produced results that were inconsistent with the original review.

Following correction of replicator errors, the main drivers of variation in the results were incomplete reporting (e.g., unclear search methods, study eligibility criteria and methods for selecting study results) and reviewer data extraction errors.

However, differences between the original reviewer’s and replicators’ summary estimates and confidence intervals were seldom meaningful.

The authors have declared no competing interest.

https://doi.org/10.1186/s13643-021-01670-0

This research was funded by an Australian Research Council Discovery Early Career Researcher Award (DE200101618), held by MJP. MJP is supported by a National Health and Medical Research Council Investigator Grant (GNT2033917). JEM is supported by a National Health and Medical Research Council Investigator Grant (GNT2009612). P-YN is supported by a Monash Graduate Scholarship and a Monash International Tuition Scholarship. JPTH is supported in part by the National Institute for Health and Care Research (NIHR203807, NIHR153861, NIHR200181). The funders had no role in the study design, decision to publish, or preparation of the manuscript.

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All data, code and materials associated with this project are publicly available on the Open Science Framework under a CC-BY license (DOI: 10.17605/OSF.IO/V3MNH).

https://www.doi.org/10.17605/OSF.IO/V3MNH