%0 Journal Article
%T Overstating the evidence ¨C double counting in meta-analysis and related problems
%A Stephen J Senn
%J BMC Medical Research Methodology
%D 2009
%I BioMed Central
%R 10.1186/1471-2288-9-10
%X Various problems in overstating the precision of results from meta-analyses are described and illustrated with examples, including papers from leading medical journals. These problems include, but are not limited to, simple double counting of the same studies, double counting of some aspects of the studies, inappropriate imputation of results, and assigning spurious precision to individual studies.Some suggestions are made as to how the quality and reliability of meta-analysis can be improved. It is proposed that the key to quality in meta-analysis lies in the results being transparent and checkable.Existing quality check lists for meta-analysis do little to encourage an appropriate attitude to combining evidence and to statistical analysis. Journals and other relevant organisations should encourage authors to make data available and make methods explicit. They should also act promptly to withdraw meta-analyses when mistakes are found.We live in an age of meta-analysis and would-be meta-analysts are constantly exhorted to find all the evidence. A popular tool for evaluating the quality of meta-analysis places great stress on the efforts that have been made to find all the relevant studies and the extent to which these efforts have been described [1,2]. Meta-analysts are advised to use funnel plots [3] or other similar devices in an attempt to establish if there has been any publication bias in favour of significant results and to calculate how many missing studies it would take to overturn their conclusions [4].The reverse problem, however, of finding evidence that isn't there has received rather less attention, yet is surely just as, if not more, serious.In this article I describe various species of this problem, illustrating it with examples from leading medical journals, including The Journal of the American Medical Association (JAMA), The British Medical Journal(BMJ), The Lancet and The New England Journal of Medicine (NEJM). There is no attempt to quantify the
%U http://www.biomedcentral.com/1471-2288/9/10