Meta-analyses: a method to maximise the evidence from clinical studies?
Evidence-based medicine (EBM) is becoming the guiding principle for clinical treatment decisions. But evidence remains a loosely defined term. Multiple criteria for evidence criteria have been proposed. Most influential evidence criteria give priority to meta-analyses because they promise an objective procedure to combine the outcomes of all informative, putatively conflicting studies on the same issue in an overall score. However, we claim that meta-analyses are of limited informative value for the following six reasons: (1) meta-analyses are often "overpowered" with clinically irrelevant results that might emerge as highly significant; (2) there is serious concern of publication biases with "negative" studies not being published; (3) meta-analyses consider the variation in the results of the empirical studies included to be random noise, however, the variability of results across studies can be informative; (4) the result of a meta-analysis depends on the strategy used to identify the included empirical studies; (5) the quality of conclusions from meta-analyses depends on the statistical tests used to combine the results of the separate studies; (6) the qualitative conclusions drawn from the meta-analytical combination of individual studies may depend on specific design aspects of the individual studies. Thus, meta-analyses are primarily a method to generate hypotheses through an a posteriori analysis of treatment effects.
Maier
Wolfgang
W
Department of Psychiatry and Psychotherapy, Rheinische Friedrich-Wilhelms-University, Sigmund-Freud-Str. 25, 53105, Bonn, Germany. Wolfgang.Maier@ukb.uni-bonn.de
Möller
Hans-Jürgen
HJ
D002986:Clinical Trials as Topic / Q000639:trends*; D019317:Evidence-Based Medicine / Q000639:trends*; D006801:Humans; D015201:Meta-Analysis as Topic