| Study ID | Effect measure | Treatment effect | 95% CI | N (intervention) | N (control) | Standard error |
| Haines 2010 | Rate ratio (calculated by review authors) | 1.26 | 0.83 to 1.90 | 12 183 | 9 853 | 0.21 |
| Tideiksaar 1993 | Rate ratio (calculated by review authors) | 0.42 | 0.15 to 1.18 | 35 | 35 | 0.53 |
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