Practicalities of using a modified version of the Cochrane Collaboration risk of bias tool for randomised and non-randomised study designs applied in a health technology assessment setting.

We describe our experience of using a modified version of the Cochrane risk of bias (RoB) tool for randomised and non-randomised comparative studies.

Objectives
To assess time to complete RoB assessment
To assess inter-rater agreement
To explore the association between RoB and treatment effect size
Methods
Cochrane risk of bias assessment was performed on a sample of full text primary reports included in a systematic review comparing operative techniques for radical prostatectomy. Inter-rater agreement was assessed using the kappa statistic.

Results
Twenty-four studies were judged as high overall RoB, 13 were judged as low RoB and 11 were unclear. The weighted Kappa value was 0.35 indicating fair agreement. The median (range) time taken to rate each study was 30 min (10–49). The effect estimate for all studies was 0.61 (95% credible interval (CrI) 0.46–0.83) and 0.73 (95% CrI 0.29–1.75) for low risk studies.

Conclusions
Although the process was time consuming, using a modified version of the RoB tool proved useful for demonstrating conservative effect estimates. That we only achieved a fair agreement between reviewers demonstrates the urgent need for further validation to improve inter-rater agreement. We suggest additional RoB levels could improve inter-rater reliability. © 2013 Crown copyright.