Do variations in allocation concealment methods influence the effects found in intervention reviews?
Version of Record online: 29 NOV 2011
© 2011 Blackwell Publishing Asia Pty Ltd and Chinese Cochrane Center, West China Hospital of Sichuan University
Journal of Evidence-Based Medicine
Volume 4, Issue 4, pages 255–258, November 2011
How to Cite
Naing, C., Hasan, S. S. and Aung, K. (2011), Do variations in allocation concealment methods influence the effects found in intervention reviews?. Journal of Evidence-Based Medicine, 4: 255–258. doi: 10.1111/j.1756-5391.2011.01156.x
- Issue online: 29 NOV 2011
- Version of Record online: 29 NOV 2011
- Accepted manuscript online: 1 NOV 2011 12:00PM EST
- Received 10 August 2011; accepted for publication 5 October 2011.
Objective (i) To explore any discrepancies in intervention effects between a set of Cochrane reviews that includes trials with liberal criteria and a set with restrictive criteria in which trials with liberal design have been removed from the review, and (ii) to suggest ways to improve the quality of evidence.
Methods A documentary analysis of three Cochrane reviews of intervention studies. The selection of the Cochrane reviews was based on a two-stage sampling. The stability of effect measures after removal of trials with liberal design was investigated.
Results In two of the three reviews, we found changes in the original effect measure of the intervention after removing the studies without allocation concealment. One of these reported an 87% greater relative risk when randomized trials with liberal design were included. In the other, the risk was 19.5% lower when randomized trials with liberal design were included.
Conclusions The instability of the effect measure indicates the importance of allocation concealment during recruitment for clinical trials. We recommend further research incorporating a large number of intervention reviews and factors other than allocation concealment.