Objective: To compare the reporting on blinding in protocols and articles describing randomized controlled trials.
Study design and setting: We studied 73 protocols of trials approved by the scientific/ethical committees for Copenhagen and Frederiksberg, 1994 and 1995, and their corresponding publications.
Results: Three out of 73 trials (4%) reported blinding in the protocol that contradicted that in the publication (e.g., "open" vs. "double blind"). The proportion of "double-blind" trials with a clear description of the blinding of participants increased from 11 out of 58 (19%) when based on publications alone to 39 (67%) when adding the information in the protocol. The similar proportions for the blinding of health care providers were 2 (3%) and 22 (38%); and for the blinding of data collectors, they were 8 (14%) and 14 (24%). In 52 of 58 publications (90%), it was unclear whether all patients, health care providers, and data collectors had been blinded. In 4 of the 52 trials (7%), the protocols clarified that all three key trial persons had been blinded.
Conclusions: The reporting on blinding in both trial protocols and publications is often inadequate. We suggest developing international guidelines for the reporting of trial protocols and public access to protocols.