Figure 2.
Risks of bias. (A) Risks of bias of the included studies. The authors reviewed each item’s risk of bias for each included study. (B) Risks of bias of individual studies. +: low risk of bias; −: high risk of bias; ?: unclear risk of bias.
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.