Reporting on blinding in trial protocols and corresponding publications was often inadequate but rarely contradictory.

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.