Figure 2.
Risk of bias summary table. “?”: unclear risk of bias; “+”: low risk of bias; “−”: high 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.