We should not pool diagnostic likelihood ratios in systematic reviews

Some authors plead for the explicit use of diagnostic likelihood ratios to describe the accuracy of diagnostic tests. Likelihood ratios are also preferentially used by some journals, and, naturally, are also used in meta-analysis. Although likelihood ratios vary between zero and infinity, meta-analysis is complicated by the fact that not every combination in R+ is appropriate. The usual bivariate meta-analysis with a bivariate normal distribution can sometimes lead to positive probability mass at values that are not possible. We considered, therefore, three different statistical models that do not suffer from this drawback. All three approaches are so complicated that we advise to consider meta-analysis of sensitivity and specificity values instead of likelihood ratios. Copyright (C) 2007 John Wiley & Sons, Ltd.