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 *

Abstract

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 by 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.