| Date | Event | Description |
|---|---|---|
| 7 August 2008 | Amended | Converted to new review format. |
| 4 September 2001 | New search has been performed | New search. First update September 2001 identified nine additional citations to nine studies; of these six were excluded from the review and three require further information from the authors. |
| 24 November 1998 | New citation required and conclusions have changed | Substantive amendment |
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