Physician interpretations and textbook definitions of blinding terminologyin randomized controlled trials

Context When clinicians assess the validity of randomized controlled trials (RCTs), they commonly evaluate the blinding status of individuals in the R CT. The terminology authors often use to convey blinding status (single, do uble, and triple blinding) may be open to various interpretations. Objective To determine physician interpretations and textbook definitions o f RCT blinding terms. Design and Setting Observational study undertaken at 3 Canadian university tertiary care centers between February and May 1999. Participants Ninety-one internal medicine physicians who responded to a sur vey. Main Outcome Measures Respondents identified which of the following groups they thought were blinded in single-, double-, and triple-blinded RCTs: par ticipants, health care providers, data collectors, judicial assessors of ou tcomes, data analysts, and personnel who write the article. Definitions fro m 25 systematically identified textbooks published since 1990 providing def initions for single, double, or triple blinding. Results Physician respondents identified 10, 17, and 15 unique interpretati ons of single, double, and triple blinding, respectively, and textbooks pro vided 5, 9, and 7 different definitions of each. The frequencies of the mos t common physician interpretation and textbook definition were 75% (95% con fidence interval [CI], 65%-83%) and 74% (95% CI, 52%-90%) for single blindi ng, 38% (95% CI, 28%-49%) and 43% (95% CI, 24%-63%) for double blinding, an d 18% (95% CI, 10%-28%) and 14% (95% CI, 0%-58%) for triple blinding, respe ctively. Conclusions Our study suggests that both physicians and textbooks vary grea tly in their interpretations and definitions of single, double, and triple blinding. Explicit statements about the blinding status of specific groups involved in RCTs should replace the current ambiguous terminology.