Clinical Trials

❘❙❚■ Chapter 38 | Meta-AnalysisThirdly, each of the studies included in the meta-analysis will have their ownproblems with internal validity [4,6]. The biases existing within each study will bepassed on to the meta-analysis and they will affect its conclusions. It is thereforeessential that study quality is considered when a preliminary literature searchis performed.Lastly, a meta-analysis is usually performed when the results of modest studiesconflict or there is a large variability in the size of the treatment effect. If datafrom large trials with matching criteria were available, a meta-analysis would notbe needed.While meta-analyses are increasingly being performed in medical research,the analysis is only as good as the team performing the work. The art of this scienceis still developing in an attempt to overcome several limitations. A strongmeta-analysis will pay careful attention to the inputs (ie, patients, endpoints, andtrial design) and will be clear about the methods and assumptions used. Finally,individuals who are contemplating performing a meta-analysis are advisedto work together with researchers and statisticians with experience in this field.ConclusionThe results of a meta-analysis can provide a significant weight of evidenceand, although the complexity of the method is a limitation, this analysis allowsclinical questions to be addressed in the absence of data from a large, definitiverandomized trial. Where evidence for the benefit of a new treatment overstandard therapy conflicts between modest-sized studies or there is variationin the size of the benefit, a meta-analysis gives a more accurate measure of thetrue effect of the therapy or intervention. Meta-analyses are therefore here tostay, and are being performed in many specialties other than healthcare. There istherefore an increasing need for researchers to be able to appreciate the place ofmeta-analyses and the results they generate, bearing in mind their complexities.References1. Shibata MC, Flather MD, Wang D. Systematic review of the impact of beta-blockers on mortalityand hospital admissions in heart failure. Eur J Heart Fail 2001;3:351–7.2. Chalmers TC. Meta-analysis in clinical medicine. Trans Am Clin Climatol Assoc 1987;99:144–50.3. DerSimonian R, Laird NM. Meta-analysis in clinical trials. Control Clin Trials 1986;7:177–86.4. Egger M, Davey Smith G, Altman D, editors. Systematic Reviews In Health Care: Meta-AnalysisIn Context. London: BMJ Publishing Group, 2001.450