Key result
Meta-analysis methodology holds potential problems with bias in location and selection of studies, as illustrated by contrasting conclusions of meta-analyses on heparins for thrombosis prevention.
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The article discusses the potential biases in the location and selection of studies for meta-analyses, illustrating the issue with conflicting meta-analyses on heparin for thrombosis prevention.
Meta-analysis has received a mixed reception since the outset. Some people have rejected what they see as exercises in “mega-silliness,”1 while the purveyors of a highly distinguished series of meta-analyses of perinatal medical care2 have been dismissed as “an obstetrical Baader-Meinhof gang.”3 To some clinicians objecting to the findings of meta-analyses, “a tool has become a weapon.”4 At the other end of the spectrum, the application of a technique that basically consists of calculating a weighted average has been hailed as “Newtonian,”5 and it has been suggested that meta-analysis has left no place for the narrative review article.6 The truth is likely to lie somewhere between these extreme views. #### Summary points That meta-analysis holds potential problems can be illustrated by contrasting the conclusions of two meta-analyses comparing low molecular weight heparins and standard heparin in the prevention of thrombosis after surgery.7 8 One group concluded that “low molecular weight …
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Egger et al. (1998) conducted a review in thrombosis after surgery. low molecular weight heparins vs. standard heparin was evaluated. Meta-analysis methodology holds potential problems with bias in location and selection of studies, as illustrated by contrasting conclusions of meta-analyses on heparins for thrombosis prevention.
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