A confirmatory study of Rasch-based optimal categorization of a rating scale.

The purpose of this study was to determine if the characteristics of the optimal categorization identified by the Rasch analysis in a previous study can be maintained when the revised scale is applied to the same population. Based on the results of the previous Rasch analysis, a 23-item exercise barrier scale was modified from its original five-category structure ("Very often" = 1, "Often" = 2, "Sometimes" = 3, "Rarely" = 4, and "Never" = 5) to a three-category structure ("Very Often" = 1, "Sometimes" = 2, and "Never" = 3). The modified scale was then mailed to the original sample (N = 381), of which 206 returned the survey; a return rate 57.5%. The data was again analyzed using the Rasch Rating Scale model. Overall, the Rasch model fit data well and similar change patterns were observed in two category statistics provided by the Rasch analysis. The order of item severity was also well kept and the correlation of item severities generated from two studies was very high, with r = .98. In addition, similar results were also found in respondents' ability estimations, and the correlation between the two studies was moderately high, with r = .68. These results verified that the characteristics of the optimal categorization identified by the Rasch post-hoc analysis can be maintained after the original scale was modified based on such an analysis.