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.
Grade of recommendation and level of evidence:
| A: Experimental or observational studies of higher consistency. |
| B: Experimental or observational studies of lower consistency. |
| C: Case reports / uncontrolled studies. |
| D: Opinion without critical evaluation, based on consensus, physiological studies or animal models. |
