Figure 1
![Figure 1](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2F1471-2334-14-S1-S6/MediaObjects/12879_2014_Article_2960_Fig1_HTML.jpg)
Selection of studies for the meta-analysis. *Inclusion/exclusion criteria as reported in the text and in additional file 1.
Selection of studies for the meta-analysis. *Inclusion/exclusion criteria as reported in the text and in additional file 1.