Evaluation of the Quality of Prognosis Studies in Systematic Reviews

21 March 2006 | Volume 144 Issue 6 | Pages 427-437

Background: To provide valid assessments of answers to prognostic questions, systematic reviews must appraise the quality of the available evidence. However, no standard quality assessment method is currently available.

Purpose: To appraise how authors assess the quality of individual studies in systematic reviews about prognosis and to propose recommendations for these quality assessments.

Data Sources: English-language publications listed in MEDLINE from 1966 to October 2005 and review of cited references.

Study Selection: 163 systematic reviews about prognosis that included assessments of the quality of studies.

Data Extraction: A total of 882 distinct quality items were extracted from the assessments that were reported in the various reviews. Using an iterative process, 2 independent reviewers grouped the items into 25 domains. The authors then specifically identified domains necessary to assess potential biases of studies and evaluated how often those domains had been addressed in each review.

Data Synthesis: Fourteen of the domains addressed 6 sources of bias related to study participation, study attrition, measurement of prognostic factors, measurement of and controlling for confounding variables, measurement of outcomes, and analysis approaches. Reviews assessed a median of 2 of the 6 potential biases; only 2 (1%) included criteria aimed at appraising all potential sources of bias. Few reviews adequately assessed the impact of confounding (12%), although more than half (59%) appraised the methods used to measure the prognostic factors of interest.

Limitations: Reviews may have been missed by the search or misclassified because of incomplete reporting. Validity and reliability testing of the authors' recommendations are required.

Conclusions: Quality appraisal, a necessary step in systematic reviews, is incomplete in most reviews of prognosis studies. Adequate quality assessment should include judgments about 6 areas of potential study biases. Authors should incorporate these quality assessments into their synthesis of evidence about prognosis.

Author and Article Information

From Institute for Work and Health, University of Toronto, and Mount Sinai Hospital, Toronto, Ontario, Canada.

Acknowledgments: The authors thank Drs. Doug Altman and Greta Ridley for valuable comments on earlier versions of this manuscript, Drs. Sheilah Hogg-Johnson and George Tomlinson for comments and discussion on the design and analysis, Evelyne Michaels for her assistance with editing and useful comments on an earlier draft of this manuscript, and Jeremy Dacombe and Quenby Mahood for assistance with literature retrieval.

Grant Support: This project was partially funded by a research grant from the Ontario Chiropractic Association and Ontario Ministry of Health and Long Term Care Special Chiropractic Research Fund. Dr. Hayden is supported by a Postdoctoral Fellowship Award from the Canadian Institutes of Health Research and Canadian Chiropractic Research Foundation. Dr. Côté is supported by a New Investigator Award from the Canadian Institutes for Health Research and by the Institute for Work and Health and the Workplace Safety and Insurance Board of Ontario. Dr. Bombardier holds a Canada Research Chair in Knowledge Transfer for Musculoskeletal Care.

Potential Financial Conflicts of Interest: None disclosed.

Requests for Single Reprints: Jill A. Hayden, DC, Institute for Work and Health, 481 University Avenue, Suite 800, 8th Floor, Toronto, Ontario M5G 2E9, Canada; e-mail, jhayden{at}iwh.on.ca.

Current Author Addresses: Drs. Hayden and Côté: Institute for Work and Health, 481 University Avenue, Suite 800, 8th Floor, Toronto, Ontario M5G 2E9, Canada.

Dr. Bombardier: Toronto General Hospital, Eaton North Wing, 6th Floor, Room 231A, 200 Elizabeth Street, Toronto, Ontario M5G 2C4, Canada.