Should study subjects see their previous responses: data from a randomized control trial.

To test the relative merits of administering questionnaires with previous responses available (the informed condition) or unavailable (the blind condition), we administered blind and informed versions of a quality of life questionnaire (the Chronic Respiratory Disease Questionnaire, or CRQ) in a randomized, double-blind trial of bronchodilators in chronic airflow limitation. The responsiveness of the two methods, as reflected in the p-values associated with salbutamol and theophylline effects were comparable for three of the four dimensions of the CRQ. The data suggested possible increased responsiveness of the informed method for the emotional function dimension of the questionnaire. Changes in the informed CRQ dyspnea and fatigue dimensions showed stronger correlations with changes in spirometry, 6 minute walk distance, and rating of dyspnea after the walk test than did blind administration. Further, changes in all four CRQ dimensions showed stronger correlations with corresponding global ratings using the informed questionnaire. These results suggest that by letting study subjects see their previous responses the validity of subjective measures of health status in clinical trials can be improved.