Aggregated measures of functional disability in a nationally representative sample of disabled people: analysis of dimensionality according to gender and severity of disability.
OBJECTIVE
To determine (i) the dimensional invariance of instrumental and basic activities of daily living (IADL/ADL) by gender subgroups, and (ii) the extent to which ADL dimensionality varies with the inclusion or exclusion of nondisabled people.


METHODS
Data were taken from the 1999 Spanish Survey on Disability, Impairment and State of Health. The analysis focussed on 6,522 people aged over 65 years who received help to perform or were unable to perform IADL/ADL items. Unidimensional and multidimensional item response theory (IRT) models were applied to this sample.


RESULTS
In the female sample, IADL/ADL items formed a scale with sufficient unidimensionality to fit a two-parameter logistic IRT model. In the male sample, the structure was bidimensional: self-care and mobility, and household activities. When the sample was composed of IADL/ADL disabled people, ADL items formed a unidimensional scale; when it was composed only of ADL disabled people, they formed a bidimensional structure: self-care and mobility.


CONCLUSIONS
IADL/ADL items can be combined in a single scale to measure severity of functional disability in females, but not in males. Separate aggregated scores must be considered for each subdomain, basic mobility and self-care, in order to measure the severity of ADL disability.
Cabrero-García
Julio
J
Department of Nursing, University of Alicante, Campus de San Vicente del Raspeig, Ap. 99, 03080 Alicante, Spain. julio.cabrero@ua.es
López-Pina
José Antonio
JA
D000203:Activities of Daily Living; D000368:Aged; D000369:Aged, 80 and over; D004185:Disability Evaluation; D006233:Persons with Disabilities; D005260:Female; D006305:Health Status Indicators; D006306:Health Surveys; D006801:Humans; D016015:Logistic Models; D008297:Male; D015233:Models, Statistical; D012720:Severity of Illness Index; D012737:Sex Factors; D013030:Spain