A comparison of seven-point and visual analogue scales. Data from a randomized trial.
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Many controlled trials rely on subjective measures of symptoms or quality of life as primary outcomes. The relative merits of different response options for these instruments is an important issue. Therefore, we compared the responsiveness and validity of seven-point versus visual analogue scales (VAS) in a questionnaire measuring quality of life in chronic heart failure in a double-masked crossover trial of digoxin versus placebo. The VAS and seven-point scale versions of the questionnaire were administered to 20 patients during 7 weeks on digoxin and 7 weeks on placebo. The order of administration of the questionnaires was determined by random allocation. The ability of the two methods to distinguish digoxin and placebo, and their correlation with other measures, were comparable. We conclude that the two methods of presenting response options show comparable responsiveness and validity in a randomized trial setting. The ease of administration and interpretation of the seven-point scale recommend its use.
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