The Academic Medical Center Linear Disability Score item bank: psychometric properties of a new generic disability measure in rheumatoid arthritis.
OBJECTIVE
To determine the psychometric properties of the Academic Medical Center (AMC) Linear Disability Scale (ALDS) item bank in a population of patients with rheumatoid arthritis (RA).


METHODS
129 patients with RA completed the ALDS and Health Assessment Questionnaire Disability Index (HAQ-DI) at baseline, and after 8 and 16 weeks of anti-tumor necrosis factor-alpha treatment. Disease activity assessments at these timepoints included serum levels of C-reactive protein, Disease Activity Score 28, morning stiffness, and visual analog scales for global disease activity and fatigue.


RESULTS
Reliability of the ALDS was excellent (homogeneity, Cronbach's alpha = 0.95; test-retest, intraclass correlation coefficient = 0.93). The ALDS results at baseline were strongly correlated with the HAQ-DI (r = -0.75). With regard to known group validity, both instruments discriminated between higher and lower disease activity (ALDS, p < 0.0001; HAQ-DI, p = 0.002) and between non-, moderate, and good responders (ALDS, p = 0.002; HAQ-DI, p < 0.0001), indicating that both instruments differentiate between groups. The ALDS was moderately to highly responsive to changes between baseline and after 8 weeks and 16 weeks of treatment (standardized response mean, range = 0.71-1.19). No substantial floor or ceiling effects were found.


CONCLUSIONS
Our results show that the ALDS is a promising new instrument, with at least equivalent psychometric properties compared to the HAQ-DI. Advantages of the ALDS item bank are its linear structure and an item bank that can be adapted depending on the ability level of the patient.
Weisscher
Nadine
N
Department of Neurology, Academic Medical Center, University of Amsterdam, The Netherlands. n.weisscher@amc.uva.nl
Wijbrandts
Carla A
CA
de Haan
Rob
R
Glas
Cees A W
CA
Vermeulen
Marinus
M
Tak
Paul Peter
PP
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000503:physiopathology* / Q000523:psychology*; D002097:C-Reactive Protein / Q000378:metabolism; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011594:Psychometrics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index
D002097:C-Reactive Protein