To the Editor.

Garrison and Christakis justify their systematic review by pointing at some presumed methodologic shortcomings of our systematic review, published in 1998. In fact, the conclusion of their review differs only slightly from ours, and we wonder if these differences can only be attributed to flaws in ours. We therefore would like to comment on the reasons why our review (according to the introduction of Garrison and Christakis' review) was thought to be inappropriate.

First, one can always argue whether studies are sufficiently homogeneous to be pooled; however, we don't agree that we actually pooled inhomogeneous studies and ask reader to compare. Second, we did pool different outcome measures, using effect sizes. Given the lack of uniformity in outcome measures, we considered this the most informative approach. Although we agree that effect sizes are difficult to translate to the clinical setting, they are often used in...

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