What does this research mean for the field?

In a double-blind trial of propranolol, blinding is partially compromised as clinic personnel can correctly identify treatment assignment in approximately 70% of cases, likely by observing heart rate changes, and patients receiving the active drug are more likely to correctly guess their assignment than those receiving placebo. Novelty: ClaimNovelty.INCREMENTAL. Consensus alignment: ConsensusAlignment.NEUTRAL.

March 22, 1985

Assessment of Double-blindness at the Conclusion of the β-Blocker Heart Attack Trial

Structured PICO

Are patients and clinic personnel able to correctly guess treatment group assignment in a double-blind trial of propranolol versus placebo?

Population

Patients and clinic personnel in the β-Blocker Heart Attack Trial

Intervention

Propranolol hydrochloride

Comparator

Placebo

Outcome

Correct identification of treatment group assignment by patients and clinic personnel

The study demonstrates that blinding in the β-Blocker Heart Attack Trial was partially compromised, with clinic personnel likely using heart rate changes to guess treatment assignment.

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.

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