Figure 2.
PRISMA diagram and eligible studies by year of publication. (a) PRISMA flow diagram of the study selection process and (b) number of included studies by year of publication.
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.