| 1A. Systematic review of RCTs (with consistent results from individual studies). |
| 1B. RCTs (of good quality). |
| 2A. Systematic review of 2B studies (with consistent results from individual studies). |
| 2B. Prospective comparative studies (or RCT of poorer quality). |
| 2C. Outcome studies (analyses of large registries, population-based data, etc.). |
| 3. Retrospective, comparative studies, case–control studies. |
| 4. Case series (i.e., studies without control group). |
| 5. Expert opinion, animal or lab experiments. |
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.