Fig 2. Risk of bias assessed in the included randomized controlled trials.
Plus-sign represents ‘low risk’, minus-sign represents ‘high risk’, empty represents ‘unclear risk’.
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.