Assessment of double-blindness at the conclusion of the beta-Blocker Heart Attack Trial

Abstract

At the conclusion of a double-blinded, randomized clinical trial of propranolol hydrochloride, but before unblinding, the patients and clinic personnel were asked to guess the treatment group assignment of each patient. While 79.9% of the patients receiving propranolol correctly identified their treatment group assignment, 57.2% of the patients receiving placebo incorrectly guessed that they were also in the propranolol group. No specific mechanism was identified to explain why more patients receiving propranolol were better able to guess their group assignment. Clinic physicians correctly identified the group assignment of 69.9% of the patients receiving propranolol and 68.8% of the patients receiving placebo. Clinic coordinators correctly identified the group assignment of 67.1% of the patients receiving propranolol and 70.6% of the patients receiving placebo. For clinic personnel, heart rate level and heart rate change seem to be the mechanisms employed to identify their patients' treatment assignment.

KIE: At the conclusion of the Beta-Blocker Heart Attack Trial (BHAT), a major research project sponsored by the National Heart, Lung, and Blood Institute, investigators conducted a survey to assess the effectiveness of the trial's double-blind design. Patients, physicians, and coordinators were asked to guess the treatment group assignment of each subject. Patients receiving the drug, propanolol, were better able to identify their assignment than those receiving a placebo. Clinic personnel were better able than the patients to differentiate between the two groups, probably due to their monitoring of patients' heart rates. The BHAT researchers concluded that, although double-blindness was not completely achieved, this fact did not influence the conduct of the trial, as no group differences in drug and visit compliance or in the use of concomitant therapy were found.