Evaluation of a multidimensional measure of dyspepsia-related health for use in a randomized clinical trial

In previous work, we developed a multidimensional measure of dyspepsia-rela ted health. To evaluate the adequacy of this instrument as an outcome measu re for a large-scale, multicenter, randomized clinical trial, we used Rasch analysis to address three questions: (1) Are the scales interval level! (2 ) Do the scales measure precisely across the entire range of dyspepsia outc omes! (3) Do the scales' items have an optimal number of response categorie s? We found that the scales were not interval-level and that they did not m easure effectively at low or high levels of the dyspepsia-related outcomes. Our results also suggest that patients were capable of discriminating amon g only four- to seven-item response categories. Further studies are needed to identify items that effectively measure high and low levels of dyspepsia -related outcomes and to validate that decreasing the number of response ca tegories improves the psychometric properties of these scales. J CLIN EPIDE MIOL 52;5:381-392, 1999. (C) 1999 Elsevier Science Inc.