Updating systematic reviews can improve the precision of outcomes: a comparative study

Objectives: The objective of this study was to investigate the main characteristics and the precision of outcomes between updated and original systematic reviews (SRs).

Study design and setting: We searched PubMed and Embase.com on 31 March 2019 and included 30 pairs of updated and original SRs. We calculated changes in outcomes and the precision of effect size estimates in updated SRs, compared with original SRs. Review Manager 5.3 software was adopted to create forest plots showing comparable outcomes.

Results: The average update time was 56.0 months, and incorporating new trials (23 SRs, 76.7%) was the main reason for the update. Compared with original SRs, 24 (80.0%) updated SRs included more randomized controlled trials and 22 (73.3%) updated SRs involved a larger number of patients. Of the 130 comparable outcomes, only three (2.3%) outcomes were observed with a significant change in three SR updates. No new data from randomized controlled trials were added to 36 (27.7%) outcomes during the update process. Of the 94 outcomes including new evidence, 83 (88.3%) showed an improvement in precision, 5 (5.3%) showed a decrease in precision, and 6 (6.4%) did not exhibit changes in precision.

Conclusion: Updating SRs could increase the precision of most comparable outcomes, although the conclusions of almost all updated SRs were similar to original SRs.