Table 4.
Levels of evidence
| Reviews of cohort studies | Level V | 5 |
| Cohort studies | Level VI | 12 |
| Research/Best Practices | Level VII | 1 |
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.