title: Rasch-built myotonic dystrophy type 1 activity and participation scale (DM1-Activ).
abstract: We describe the development of an outcome measure of activity and participation for patients with myotonic dystrophy type 1 using the Rasch measurement model. A 49-item questionnaire was completed by 163 DM1 patients. Data were subsequently analyzed with Rasch software to design the item set to fit model expectations. Through systematic investigation of response category ordering, model fit, item bias, and local response dependency, we succeeded in constructing a 20-item unidimensional scale of activity and participation (DM1-Activ). High internal consistency (PSI=0.95) and good test-retest reliability values of item difficulty hierarchy and patient location were demonstrated. Patient measures had acceptable correlations with MRC sum scores and MIRS grades (ICC=0.69 and 0.71, respectively), indicating good external construct validity. DM1-Activ is a practical, reliable and valid outcome measure that fulfils all clinimetric requirements. Further evaluation of this scale is needed to provide a nomogram for clinical use.
authors.affiliation: Department of Neurology, Maastricht University Medical Centre, P.O. Box 5800, 6202 AZ, Maastricht, The Netherlands. m.hermans@mumc.nl
authors.forename: Mieke C E
authors.initials: MC
authors.lastname: Hermans
authors.forename: Catharina G
authors.initials: CG
authors.lastname: Faber
authors.forename: Marc H
authors.initials: MH
authors.lastname: De Baets
authors.forename: Christine E M
authors.initials: CE
authors.lastname: de Die-Smulders
authors.forename: Ingemar S J
authors.initials: IS
authors.lastname: Merkies
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D015982:Bias; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009223:Myotonic Dystrophy / Q000175:diagnosis* / Q000503:physiopathology*; D017063:Outcome Assessment, Health Care; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D055815:Young Adult