Table 1.
Methodology
| Number of papers | |
|---|---|
| Population survey | 12 |
| Cohort (observational) | 13 |
| Case–control | Four, plus two nested |
| Social science | 5 |
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.