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Risk of bias summary: review authors' judgements about each risk of bias item for each included study.
| Random sequence generation (selection bias) | Allocation concealment (selection bias) | Blinding of participants and personnel (performance bias) | Incomplete outcome data (attrition bias) | Selective reporting (reporting bias) | Other bias | |
|---|---|---|---|---|---|---|
| Donohue et al. 2002 [7] | + | + | + | + | ||
| Donohue et al. 2005 [1] | + | + | + | − | ||
| Özdal et al. 2005 [10] | + | + | + | |||
| Sandfeldt et al. 2001 [11] | + | + | + | + |
