| Study ID | Effect measure | Treatment effect | 95% CI | N (intervention) | N (control) | Standard error |
| Haines 2010 | Rate ratio (calculated by review authors) | 0.69 | 0.35 to 1.34 | 12 183 | 9 853 | 0.35 |
| Tideiksaar 1993 | Rate ratio (calculated by review authors) | 0.25 | 0.03 to 2.24 | 35 | 35 | 1.12 |
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