| Date | Event | Description |
|---|---|---|
| 15 February 2012 | Amended | 'Declaration of interest' and 'Contributions of authors' updated; no other changes to text. |
| 15 February 2012 | New citation required but conclusions have not changed | Change in listing of authors to include Dr WL van der Pol. This corrects an error in the authorship of this update. |
| 31 March 2011 | New citation required but conclusions have not changed | RI Wadman included as new lead author. |
| 8 March 2011 | New search has been performed | Databases were searched and review was updated. Two new trials were found. |
| 30 July 2008 | Amended | Converted to new review format. |
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