, Volume 26, Issue 5, pp 802-803
Date: 01 Jun 2012

Internal validity and the risk of bias: a case for a comprehensive review

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To the Editor:

Zambon et al. [1] appraised the quality of a series of meta-analyses, and found that “Internal validity appeared largely robust, as most (50.5 %) reviews were at low risk for bias.” To conclude that there is a low risk of bias, a comprehensive review is required, so that all potential biases are considered. Otherwise, we might as well notice that some raindrops have missed us as we run through the rain, and conclude, on that basis, that therefore we must be dry. This wishful thinking provides a false sense of security that interferes with required reforms, and is potentially quite harmful. So how many raindrops were observed to miss us? The authors assessed internal validity based on: (1) search strategies; (2) study selection; (3) inclusion of only (masked) randomized trials; (4) evaluation of study homogeneity; and (5) reporting of conflicts and funding. It is rather unnerving, given that randomized trials are the worst possible design except for all the rest [2], that ...