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.
The risk ratios (RRs) were determined using the Mantel-Haenszel random-effects model. Square data markers represent RRs, with marker size reflecting the statistical weight of the study using random-effects meta-analysis; horizontal lines, 95% CIs; diamond, the overall RR and 95% CI for the outcome of interest.
