Who are we blinding? A systematic review of blinded clinical trials

Background: The terms much greater than double blind (masked)much less than and much greater than single blind much less than are often used to mean d ifferent things in reports of blinded clinical trials of non-pharmaceutical interventions. Objective: To investigate the discordance in usage of the terms much greate r than double blindo and much greater than single blind much less than in n on-pharmaceutical clinical trials. Methods: A computerized literature search was conducted in Medline (1997 to April 2000). journals were chosen that deemed likely to contain non-pharma ceutical RCTs and that had the highest Impact Factor. Search terms used wer e much greater than double-blind much less than and much greater than singl e blindo. Articles were included in the review if they reported prospective randomised controlled trials of non-pharmaceutical interventions using the term much greater than double blind much less than or much greater than si ngle blind much less than. Assessment of the blinding was performed indepen dently by two authors, who recorded the presence of details of the blinding of four possible parties: subjects (participants, patients), therapists (i ntervention givers), assessors (evaluators), and data analysts. The consist ency in the use of terminology in eachjournal was also investigated. No ass umptions were made, but specific confirmatory statements by the authors wer e sought in the text. Results. A total of 48 articles from 17 journals were included for data ext raction, 25 in the double blind, and 23 in the single blind category. The l etters S, A, T, D represents subject (S), assessor (A), therapist (T), data analyst (D) blinding. In the studies labeled as much greater than double b lindo, blinding was performed as follows: two used SATD blinding; five blin ded SAT; seven SAD; nine SA; two S only; no study was not blinded in at lea st one respect. In the studies labeled much greater than single blind much less than, one study blinded SAD; five SA; one ST; two AD; one S; eleven A; one D; no study blinded T; and one study used no blinding at all. Differen t types of blinding within identically labeled studies and discordant termi nology using same blinding design was found. In five journals, the use of m uch greater than double blind much less than and much greater than single b lindo was inconsistent. Conclusion: There is clear discordance in the usage of the terms much great er than double blind much less than and much greater than single blind much less than in the reports of non- pharmaceutical randomised controlled tria ls published in high quality journals. We suggest that reports should expre ssly state which parties were blinded.