Quality-Days Incrementally Gained: A New Approach for Short-Term Evaluations Based on the Extended Q-TWiST Method Illust
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0092-8615/2oo0 Copyright 0 ZOO0 Drug Information Association Inc.
QUALITY-DAYS INCREMENTALLY GAINED: A NEW APPROACH FOR SHORT-TERM EVALUATIONS BASED ON THE EXTENDED Q-TWiST METHOD ILLUSTRATED IN A CLINICAL STUDY OF REFLUX DISEASE PATIENTS* DAVEP. MILLER,MS, DAVIDJ. PASTA,MS, SUSAND. MATHIAS,MPH
AND
The Lewin Group, San Francisco, California
HILARYH. COLWELL, MPH The National Alliance of Breast Cancer Organizations, New York, New York
JAMESM. HENNING, MS TAP Holdings Inc., Deerfield, Illinois
Objective: The objective of this study was to derive a measure of quality-time to be used in treatment evaluations for gastroesophageal reflux disease (reflux disease). Specifically, we sought to refine the Extended Quality-adjusted Time without Symptoms and Toxicities (Q-TWiST) approach and propose a new measure, called Quality-Days Incrementally Gained (QDIG). Design: One hundred and sixty-seven patients with reflux disease randomized to one of two treatments completed a health-related quality-of life questionnaire at baseline and after four and eight weeks of treatment. The questionnaire contains generic and reflux disease-specific measures and corresponding importance items. The weighted assessment score, fundamental to calculating both the Extended Q-TWiST and the QDIG, was computed using several weighting schemes to determine the most robust and appropriate statistic. Main Outcome Measures and Results: The Extended Q-TWiST was affected b y the relative weighting of baseline and follow-up weighted assessment score. The QDIG directly discounts the baseline score and showed the greatest sensitivity to treatment differences. The variance in the Extended Q-TWiST and QDIG were both reduced by using importance weights carried forward from baseline rather than time-varying importance weights, and by using population-weights rather than individual person weights. Conclusions: Careful consideration should be made when deciding to use the Extended Q-TWiST or QDIG approach. Our data suggest the QDIG approach is superior in studies of short duration with heterogeneous populations. Key Words: Quality-of-life;Q-TWIST; Multiple endpoints; Reflux disease; Lansoprazole *This study was supported by TAP Holdings Inc. Reprint address: Dave P. Miller, MS, Director, Data Analysis, The Lewin Group, 490 Second Street, Suite 201, San Francisco, CA 94107. E-mail: [email protected].
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D. P. Miller, D. J. Pasta, S. D. Mathias, H. H. Colwell, and J. M . Henning
INTRODUCTION THE IDEAL ANALYSIS for comparing the health-related quality-of-life (hereafter QOL) of two treatments would reduce the results to a single value indicating the direction and magnitude of the difference between the treatments, together with some information about the variability of the estimate. One impediment to obtaining a single-number summary is that measurements are generally taken at multiple points in time. This difficulty can be easily addressed by calculating the area under the curve. A
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