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.
Evidence grade classification according to GRADE [53]
| Level of evidence | Type of study |
|---|---|
| Ia | Evidence based on meta-analyses of randomized controlled trials in systematic reviews |
| Ib | Evidence based on at least one randomized controlled trial |
| IIa | Evidence based on at least one well-designed controlled trial without randomization |
| IIb | Evidence based on at least one well-designed, quasi-experimental study |
| III | Evidence based on well-designed, nonexperimental cohort studies |
| IV | Expert opinion |
