THE USE AND MISUSE OF METAANALYSIS

Objective-To demonstrate how the results of a meta-analysis can confus e rather than clarify therapeutic dilemmas if clinical heterogeneity a mong trials is ignored. Then to further discuss the qualities emergenc y physicians should expect from published meta-analyses if they are to affect clinical practice. Subjects and methods-The data and results w ere examined from 23 randomised controlled trials of selective deconta mination of the digestive tract (SDD), which have been combined in a p revious meta-analysis. These were reviewed to take account of clinical heterogeneity, particularly with regard to severity of patient illnes s. Results-Severity of patient illness predicts degree of reduction in mortality with SDD in a regression analysis: log odds ratio (OR) of d eath with SDD = -0.0074 - (0.0035 x control group mortality rate), P = 0.017. This is also true when trials are stratified into more and les s severely ill patients: pooled OR (a) for CMR > 41% = 0.69 (0.54 to 0 .89), with (b) CMR < 37% = 1.02 (0.86 to 1.21). This difference was no t suggested by the original meta-analysis result. Conclusions-Failure to take account of clinical heterogeneity between trials can mean a me ta-analysis result ignores important differences in the effect of a tr eatment on different groups of patients. The discussion indicates how emergency physicians might guard against basing clinical practice on m isleading meta-analysis results.