How Quickly Do Systematic Reviews Go Out of Date? A Survival Analysis

21 August 2007 | Volume 147 Issue 4

Background: Systematic reviews are often advocated as the best source of evidence to guide clinical decisions and health care policy, yet we know little about the extent to which they require updating.

Objective: To estimate the average time to changes in evidence that are sufficiently important to warrant updating systematic reviews.

Design: Survival analysis of 100 quantitative systematic reviews.

Sample: Systematic reviews published from 1995 to 2005 and indexed in ACP Journal Club. Eligible reviews evaluated a specific drug or class of drug, device, or procedure and included only randomized or quasi-randomized, controlled trials.

Measurements: Quantitative signals for updating were changes in statistical significance or relative changes in effect magnitude of at least 50% involving 1 of the primary outcomes of the original systematic review or any mortality outcome. Qualitative signals included substantial differences in characterizations of effectiveness, new information about harm, and caveats about the previously reported findings that would affect clinical decision making.

Results: The cohort of 100 systematic reviews included a median of 13 studies and 2663 participants per review. A qualitative or quantitative signal for updating occurred for 57% of reviews (95% CI, 47% to 67%). Median duration of survival free of a signal for updating was 5.5 years (CI, 4.6 to 7.6 years). However, a signal occurred within 2 years for 23% of reviews and within 1 year for 15%. In 7%, a signal had already occurred at the time of publication. Only 4% of reviews had a signal within 1 year of the end of the reported search period; 11% had a signal within 2 years of the search. Shorter survival was associated with cardiovascular topics (hazard ratio, 2.70 [CI, 1.36 to 5.34]) and heterogeneity in the original review (hazard ratio, 2.15 [CI, 1.12 to 4.11]).

Limitation: Judgments of the need for updating were made without involving content experts.

Conclusions: In a cohort of high-quality systematic reviews directly relevant to clinical practice, signals for updating occurred frequently and within a relatively short time.

Editors' Notes Context Clinicians rely on systematic reviews for current, evidence-based information. Contribution This survival analysis of 100 meta-analyses indexed in ACP Journal Club from 1995 to 2005 found new evidence that substantively changed conclusions about the effectiveness or harms of therapies occurred frequently within relatively short time periods. The median survival time without substantive new evidence for the meta-analyses was 5.5 years. Significant new evidence was already available for 7% of the reviews at the time of publication and became available for 23% within 2 years. Implication Clinically important evidence that alters conclusions about the effectiveness and harms of treatments can accumulate rapidly. —The Editors

 

Author and Article Information

From the Ottawa Health Research Institute, University of Ottawa, Chalmers Research Group, and Children's Hospital of Eastern Ontario Research Institute, Ottawa, Ontario, Canada.

Disclaimer: The authors of this report are responsible for its content. Statements in the report should not be construed as endorsement by the Agency for Healthcare Research and Quality or the U.S. Department of Health and Human Services.

Acknowledgments: The authors thank Keith O'Rourke for statistical advice, Jessie McGowan and Tamara Rader for assistance with searches, and Alison Jennings for assistance with development of the meta-analytic worksheet. They also gratefully acknowledge Dr. David Atkins and the members of the technical advisory panel for the project funded by the Agency for Healthcare Research and Quality from which this work derives: Drs. Paul Shekelle, Evelyn Whitlock, Cynthia Mulrow, Doug Altman, Martin Eccles, and P.J. Devereaux.

Grant Support: By the Agency for Healthcare Research and Quality, U.S. Department of Health and Human Services (contract no. 290-02-0021). Dr. Shojania received additional salary support from the Government of Canada Research Chairs program. Dr. Moher is the recipient of a University of Ottawa Research Chair.

Potential Financial Conflicts of Interest: None disclosed.

Reproducible Research Statement: The data set is available to interested readers by contacting Dr. Shojania (e-mail, kshojania{at}ohri.ca); statistical code can be obtained from Mr. Doucette (e-mail, sdoucette{at}ohri.ca).

Requests for Single Reprints: Kaveh G. Shojania, MD, The Ottawa Hospital–Civic Campus, 1053 Carling Avenue, Room C403, Box 693, Ottawa, Ontario K1Y 4E9, Canada; e-mail, kshojania{at}ohri.ca.

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