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.
(Chi2 = chi square statistic, CI = confidence interval, df = degrees of freedom, I2 = I-square heterogeneity statistic, IV = inverse variance, RR = risk ratio, Z = Z-statistic).
