Flow diagram of the selection of articles through study.

<p><b>from:</b> Moher D, Liberati A, Tetzlaff J, Altman DG, The PRISMA Group (2009). Preferred Reporting Items for Systematic Reviews and Meta-Analyses: The PRISMA Statement. PLoS Med 6(6): e1000097. doi:<a href="http://dx.doi.org/10.1371/journal.pmed1000097" target="_blank">10.1371/journal.pmed1000097</a></p>