In Reply: We agree with Dr Laheij that exploration
of heterogeneity sources may provide valuable information, especially for
controversial medical topics for which therapeutic or preventive effects of
different magnitude are obtained by different study designs.1
We also agree that empirical meta-analytic evaluations can be applied in other
types of studies as well.
Dr Theodoropoulos and colleagues reduce meta-analysis to a method that
simply lumps information and biases. We do not share this view. Meta-analysis
has the potential to systematically examine the strengths and weaknesses of
the accumulated evidence, explore heterogeneity between studies (including
those of different designs), and identify potential biases. As a form of original
research, meta-analysis does not compete with or substitute for other original
work. It functions at a different level than single original studies and has
been widely accepted as the highest level in the hierarchy of evidence.2,3 We welcome criticism of meta-analysis,
which may help refine further its methods. However, when a meta-analysis shows
that no more research is needed or that there are overt biases that should
be appropriately corrected, then it is equivalent to misconduct to perform
further clinical studies or to conduct new studies without correcting known
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