Reconstructing the Rasch-Built Myotonic Dystrophy Type 1 Activity and Participation Scale

Introduction A previously published Rasch-built activity and participation scale specifically designed for patients with myotonic dystrophy type 1 (DM1) was criticized for having been constructed in a relatively small cohort of patients and containing items too broadly phrased for DM1 patients, thus hampering its clinical use. Methods We report the results of the reconstructed Rasch-built DM1 activity and participation scale for clinical use (DM1-Activ(C)) through Rasch analyses using an expanded questionnaire containing 146 more simply phrased activity and participation inquiries completed by 340 patients with DM1. Results Through stepwise investigation including data quality control, model fit, response category ordering, local dependency and item bias, we succeeded in reconstructing the DM1-Activ(C) consisting of 25 items that showed good Rasch model fit, including construct convergent validity, items' weights and persons' locations reliability, and unidimensionality. Conclusion The DM1-Activ(C) scale has been reconstructed and fulfills all modern clinimetric requirements. Its use is recommended in future longitudinal trials in patients with DM1 to determine its responsiveness.