Figure 2.
Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow chart for literature published March 1, 2011, through November 30, 2016, and limited search of earlier literature.
KQ, key question..
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.