| Date | Event | Description |
|---|---|---|
| 12 March 2012 | New search has been performed | The most recent search was in January 2012. In this updated version of the review, we have included nine new studies in addition to the seven included in previous versions. |
| 12 March 2012 | New citation required but conclusions have not changed | The main conclusions of the review have not changed but we have added new comparisons and analysis. |
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.