Development and psychometric analysis of the Duchenne muscular dystrophy Functional Ability Self-Assessment Tool (DMDSAT).
The objective of this study was to describe the development and initial psychometric analysis of the UK English version of the Duchenne muscular dystrophy Functional Ability Self-Assessment Tool (DMDSAT), a patient-reported outcome (PRO) scale designed to measure functional ability in patients with Duchenne muscular dystrophy (DMD). Item selection was made by neuromuscular specialists and a Rasch analysis was performed to understand the psychometric properties of the DMDSAT. Instrument scores were also linked to cost of illness and health-related quality of life data. The administered version, completed by 186 UK patient-caregivers pairs, included eight items in four domains: Arm function, Mobility, Transfers, and Ventilation status. These items together successfully operationalized functional ability in DMD, with excellent targeting and reliability (Person Separation Index: 0.95; Cronbach's α: 0.93), stable item locations, and good fit to the Rasch model (mean person/item fit residual: -0.21/-0.44, SD: 0.32/1.28). Estimated item difficulty was in excellent agreement with clinical opinion (Spearman's ρ: 0.95) and instrument scores mapped well onto health economic outcomes. We show that the DMDSAT is a PRO instrument fit for purpose to measure functional ability in ambulant and non-ambulant patients with DMD. Rasch analysis augments clinical expertise in the development of robust rating scales.
OptumInsight, Stockholm, Sweden; Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden. Electronic address: erik.landfeldt@ki.se.
Erik
E
Landfeldt
Newcastle University John Walton Muscular Dystrophy Research Centre and MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle upon Tyne, UK.
Anna
A
Mayhew
Newcastle University John Walton Muscular Dystrophy Research Centre and MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle upon Tyne, UK.
Michelle
M
Eagle
Medical Management Centre, Department of Learning, Informatics, Management and Ethics, Karolinska Institutet, Stockholm, Sweden.
Peter
P
Lindgren
GlaxoSmithKline, NC, USA.
Christopher F
CF
Bell
Newcastle University John Walton Muscular Dystrophy Research Centre and MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle upon Tyne, UK.
Michela
M
Guglieri
Newcastle University John Walton Muscular Dystrophy Research Centre and MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle upon Tyne, UK.
Volker
V
Straub
Newcastle University John Walton Muscular Dystrophy Research Centre and MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle upon Tyne, UK.
Hanns
H
Lochmüller
Newcastle University John Walton Muscular Dystrophy Research Centre and MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle upon Tyne, UK.
Katharine
K
Bushby
D000203:Activities of Daily Living; D000293:Adolescent; D000328:Adult; D017028:Caregivers; D002648:Child; D002675:Child, Preschool; D059026:Diagnostic Self Evaluation; D005260:Female; D006801:Humans; D008297:Male; D020388:Muscular Dystrophy, Duchenne / Q000175:diagnosis* / Q000191:economics; D011594:Psychometrics; D011788:Quality of Life; D011795:Surveys and Questionnaires; D055815:Young Adult
Costs; Functional ability; Patient-reported outcome; Rasch analysis; Rating scale; Utilities