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Integrating Heterogeneous Pieces of Evidence in Systematic Reviews

Cynthia Mulrow, MD, MSc; Peter Langhorne, PhD, MRCP; and Jeremy Grimshaw, MBChB, MRCGP
[+] Article and Author Information

From the University of Texas Health Science Center at San Antonio and Audie L. Murphy Veterans Affairs Hospital, San Antonio, Texas; Royal Infirmary, Glasgow, Scotland; and the University of Aberdeen, Aberdeen, Scotland. Acknowledgments: The authors thank Drs. Robert Fletcher and Brian Haynes for their critical reading of the manuscript. They also thank the clinical reviewer, Norman J. Wilder. Requests for Reprints: Cynthia D. Mulrow, MD, MSc, Audie L. Murphy Memorial Veterans Hospital, 7400 Merton Minter Boulevard (11C6), San Antonio, TX 78284. Current Author Addresses: Dr. Mulrow: Audie L. Murphy Memorial Veterans Hospital, 7400 Merton Minter Boulevard (11C6), San Antonio, TX 78284.


Copyright ©2004 by the American College of Physicians


Ann Intern Med. 1997;127(11):989-995. doi:10.7326/0003-4819-127-11-199712010-00008
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Researchers preparing systematic reviews often encounter various types of evidence, which can generally be categorized as direct or indirect.The former directly relates an exposure, diagnostic strategy, or therapeutic intervention to the occurrence of a principal health outcome. Evidence is indirect if two or more bodies of evidence are required to relate the exposure, diagnostic strategy, or intervention to the principal health outcome.

Heterogeneity of data sources complicates integration of both direct and indirect evidence.Participants in different studies may have a wide spectrum of baseline risk and sociodemographic and cultural characteristics. A variety of formulations and intensities of exposures, diagnostic strategies, and interventions, as well as diversity in the selection and definition of control groups, may be encountered. Outcome measures may be different, and similar outcomes may be measured or reported differently. Heterogeneity of study designs and of methodologic features and quality within a given design may be found. The effective integration of direct and indirect evidence requires development of explicit models that serve as analytic frameworks for linking the important pieces of evidence. A model can be viewed as a series of subquestions, with each important subquestion warranting a systematic review. Several subjective and quantitative methods can then be used to integrate the evidence. Tabular displays of major findings and strength of evidence for each subquestion can help reviewers, patients, and providers to integrate the differing research findings and draw reasonable conclusions. Various quantitative techniques, such as decision analysis and the confidence profile method, are also available. No single integration approach is clearly superior, none obviates uncertainty, and all underscore the role of careful judgment in integrating evidence.

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Figure 1.
Model examining rationale for screening for hearing impairment.

The following are focused questions associated with some of the linkages shown. Linkage 2: What is the accuracy of screening tests (whispered voice, tuning fork, finger rub, questionnaires, audioscope) for identifying elderly patients with hearing impairments? Linkage 3: What adverse effects from mislabeling result from measuring hearing impairment in elderly patients with previously undetected hearing impairment? Linkage 4: Does treating hearing-impaired elderly patients by using hearing aids improve the acuity of hearing?.

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Figure 2.
An evidence model for the pharmacologic treatment of obesity.

The following are focused questions associated with some of the linkages shown. Linkage 7: Does the effect of pharmacologic agents on abdominal or visceral fat lead to improved lipoprotein levels? Linkage 8: Does the effect of pharmacologic agents on abdominal or visceral fat affect control of blood sugar? Linkage 9: Does the effect of pharmacologic agents on abdominal or visceral fat affect control of blood pressure? Linkage 10: Does pharmacologic treatment of obesity affect control of blood pressure independently of its effect on weight or abdominal or visceral fat?.

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Citing articles are presented as examples only. In non-demo SCM6 implementation, integration with CrossRef’s "Cited By" API will populate this tab (http://www.crossref.org/citedby.html).

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