 This study aimed to revise CQS2-slash criterion 2 which concerns allocation concealment assessment for prospective, controlled clinical trials. A meta-analysis of trials with an adequate allocation concealment was conducted and found to be homogeneous. Based on these findings, criteria for adequate allocation concealment were derived. These criteria were then incorporated into the CQS2-slash criterion 2, resulting in the revision of CQS2-B. This article was authored by Stefan Mikonach, Stefan Mikonach and Virasamy Yengapal.