Towards a proposal for assessment of blinding success in clinical trials: up-to-date review.

The CONSORT statement recommended that investigators should clearly report which key trial persons were blinded to treatment allocation and test for the success of blinding. Clinical researchers, however, more often than not overlook the assessment of the success of blinding. The severe under-reporting on the success of blinding may improve with awareness of existing quantitative methods. The two statistical methods, James' blinding index (BI) and Bang's BI, are currently available. Subjects could be asked to guess their treatment assignment, possibly with an option to express the degree of certainty. Assessments of blinding at various points may serve different purposes, i.e. to evaluate comparability between experimental versus control treatments before the trial by the third party; to examine further comparability and credibility of the control treatment and patients' expectation about treatment received in early stage of the trial, and to summarize the overall maintenance of the blinding success at the end of the trial. In this article, we review BIs and how to use these methods along with discussion of other issues in blinding assessment and reporting. We contend the two BIs that were independently developed but carry complementary properties would characterize blinding behaviours in clinical trials qualitatively as well as quantitatively, and may also shed some lights on the interpretation of the study findings. Finally we urge the Item 11b of the CONSORT statement to be revised to require the assessment/reporting of blinding success for all trials that adopt blinding schemes.