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.
Categories of evidence
| Categories of evidence | |
|---|---|
| Ia | Meta-analysis of randomized controlled trials (RTC) |
| Ib | At least one RTC |
| IIa | At least one controlled study without randomization |
| IIb | At least one other type of study |
| III | Non-experimental descriptive studies |
| IV | Expert committee reports or opinions or clinical experience of respected authorities |
