Figure 2.
(A) The risk of bias graph. (B) Risk of bias of included randomized controlled trials. +, no bias; –, bias; ?, bias unknown.
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.