Validity was assessed using the following 10 criteria:
1. Clarity of objectives.
2. Search methods.
3. Method of randomisation.
4. Blinding.
5. Description of statistical analysis.
6. Inclusion/exclusion criteria.
7. Similarities of patients between groups.
8. Management of drop-outs.
9. Management of follow-up.
10. Reporting of secondary outcomes.
Two reviewers independently assessed the validity of studies using the 10 pre-defined quality criteria. Items were scored using 2 points for yes, 1 point for partial and 0 points for no. For items relating to randomisation, a score of 0 was assigned if the study was not randomised and not blinded. All other possible responses to these criteria were assigned a score of 1. The possible range of scores was 0 to 18. The scores were calculated for each reviewer and any disagreements resolved through discussion.