Figure 1.
PRISMA flow chart of the selection process used to identify studies eligible for pooling.
Abbreviation: RCT, randomized controlled trial.
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.