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Chapter 11

Evidence-based medicine and meta-analysis: getting more out of the literature. Chapter 11. Evidence Based Medicine. First coined in 1992, Evidence Based Medicine Working Group

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Chapter 11

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  1. Evidence-based medicine and meta-analysis: getting more out of the literature Chapter 11

  2. Evidence Based Medicine • First coined in 1992, Evidence Based Medicine Working Group • Many organizations in the United States-including government agencies and the National Institutes of Health, professional medical societies, and health care payers and managed care companies-have embraced the EBM approach • Formalizes the principles and methods of reviewing and synthesizing evidence that have been developing over several decades • This chapter focuses on systematic reviews and meta-analysis

  3. 11.1 Systematic reviews and meta-analysis • systematic review • comprehensive, rigorous, and unbiased review and synthesis of up-to-date evidence provides the most reliable information to inform health practice • meta-analysis • a systematic review that uses statistical methods to combine results across several studies to address specific questions • MEDLINE currently indexes over 13,000 items under the medical subject heading of "meta-analysis."

  4. FIGURE I I-I Standard forest plot (left panel) and a cumulative meta-analysis (right panel ) of intravenous streptokinase therapy for acute myocardial infarction; see text for explanation (Reproduced with permission from the New England Journal of Medicine ) (Lauer al. 1992 )

  5. 11.2 Methodologies of systematic review and meta-analysis • Traditional narrative review articles • etiology, pathology, methods of diagnosis, range of treatment s available, and prognosis • Systematic reviews • seeks to answer one or several well-focused research question (s) rather than attempting to provide a broad overview of a topic • Systematic reviews have covered health care interventions, evaluated diagnostic tests, and assessed the association of factors with clinical conditions or outcomes • follows a well-defined protocol

  6. 11.3 Developing a systematic review protocol • Systematic reviews and meta-analyses generally are retrospective analyses of published data • A protocol should clearly describe the specific research question(s), literature search strategy, selection criteria, approach to critical appraisal of the studies, methods of statistical analyses, and interpretation of the results

  7. 11.4 Formulating the research question • The most critical step in any systematic review or meta-analysis • PICO approach (Counsell 1997) • Population, Intervention, Comparator, Outcome • Iterative process, involves a compromise to create a question that is answerable by available evidence • Provide data for decision analysis (Jordan and Lau 2003)

  8. FIGURE 11-2 Analytic framework concerning the effect of omega-3 fatty acid exposure (as supplement or from food sources) on cardiovascular disease. Population of interest in top rectangles; exposure in oval; outcomes in rounded rectangles; effect modifiers in hexagon. This connecting lines indicate associations and effects reviewed in this report. Lists in smaller font indicate the specific factors reviewed.

  9. 10.5 Literature search • Comprehensive • All relevant literature should be reviewed • Generally begins with MEDLINE • free, readily available electronically, indexes over 4,000 medical journals • Can be searched using standard search terms and Boolean operators • Update quarterly • Cochrane Central Register of Controlled Trials • Indexed over 400,000 controlled trials • EMBASE – minor • Non-English language articles - minor

  10. 10.6 Data extraction • Must be extracted from the original studies • Reliability issue : two separate extraction • Include information pertaining to the PICO parameters and methodological issues pertaining to the design and conduct of a study • Data are not standardized, and important information is often missing • The same information may be reported inconsistently within a study

  11. 10.7 Assessing the quality of studies • Conclusions drawn from systematic reviews should be based on good quality of studies • Moher et al, 1995 • “The confidence that the trial design, conduct, and analysis has minimized or avoided biases in its treatment comparison.” • Poor quality studies report exaggerated effect size • No true reference standard to determine quality

  12. 10.8 Combining data in a meta-analysis • Combine data to address a specific question • Sufficient data • Meeting inclusion criteria • Weighted average of the effect size • By combining data using a fixed-effect or a random-effects model

  13. 10.9 Exploring heterogeneity with subgroup and meta-regression analyses • No two studies are identical • Subgroups within individual studies → too small • Combine similarly defined subgroups across several studies • Meta-regression • A regression analysis to access the relationship between the treatment effects and the study characteristics • Key risk factors vary across patients and can be measured only as aggregate values

  14. 11.10 Issues in conducting meta-analysis • 11.10.1 Publication bias • Unpublished studies with negative results threaten the validity of a meta-analysis • Inverted funnel plot • Large trial vs. meta-analysis of small trials • Large clinical trials often are considered as the definitive last word in clinical evidence • Disagreement between large trials and the corresponding meta-analysis of small trials occur in about 10 to 30 percent of meta-analysis

  15. 11.10 Issues in conducting meta-analysis • 11.10.2 Large trial vs. meta-analysis of small trials • Large clinical trials often are considered as the definitive last word in clinical evidence • Disagreement between large trials and the corresponding meta-analysis of small trials occur in about 10 to 30 percent of meta-analysis

  16. FIGURE 11-3 Factors that contribute to the observed treatment effects in a randomized controlled trial.

  17. FIGURE 11-4 estimated treatment effect in a meta-analysis.

  18. 11.10.3 Updating systematic reviews and meta-analysis • Most systematic reviews and meta-analysis • Published in peer-reviewed printed journals • New publication → obsolete old one • Even after a treatment has been found to be efficacious, new trials may still need to be conducted

  19. 11.11 Uses of systematic reviews and meta-analysis • Evidence in clinical medicine • Interventions > diagnosis • Associations of factors with health outcomes

  20. 11.12 Accessing systematic reviews and meta-analyses and related products • Journals in MEDLINE • The Cochrane Library • AHRQ (Agency for Healthcare Research and Quality) • NGC (National Guideline Clearinghouse) • www.guidelines.gov

  21. 11.13 Conclusion • The number of publications and Web sites with information on EBM has rapidly increased • no longer debates on whether systematic reviews are useful or whether meta-analysis is a valid statistical method • However, their limitations must be recognized

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