Fig. 1.
PRISMA chart. *One study, Szabo et al., 2007, removed from analysis following consideration of reviewers' comments.
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.