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.
| Level I: At least 1 properly conducted randomized controlled trial, systematic review, or meta-analysis |
| Level II: Other comparison trials, non-randomized, cohort, case-control, or epidemiologic studies, and preferably more than 1 study |
| Level III: Expert opinion or consensus statement |
Adapted from the Canadian Task Force on the Periodic Health Examination.38
