Evaluation of an activities of daily living scale for adolescents and adults with developmental disabilities.

Background: Activity limitations are an important and useful dimension of disability, but there are few validated measures of activity limitations for adolescents and adults with developmental disabilities.

Objective/hypothesis: To describe the development of the Waisman Activities of Daily Living (W-ADL) Scale for adolescents and adults with developmental disabilities, and systematically evaluate its measurement properties according to an established set of criteria.

Methods: The W-ADL was administered among four longitudinally studied groups of adolescents and adults with developmental disabilities: 406 with autism; 147 with fragile-X syndrome; 169 with Down syndrome; and 292 with intellectual disability of other or unknown origin. The W-ADL contains 17 activities and each is rated on a 3-point scale (0 = "does not do at all", 1 = "does with help", 2 = "independent"), and a standard set of criteria were used to evaluate its measurement properties.

Results: Across the disability groups, Cronbach's alphas ranged from 0.88 to 0.94, and a single-factor structure was most parsimonious. The W-ADL was reliable over time, with weighted kappas between 0.92 and 0.93. Criterion and construct validity were supported through substantial associations with the Vineland Screener, need for respite services, caregiving burden, and competitive employment. No floor or ceiling effects were present. There were significant group differences in W-ADL scores by maternally reported level of intellectual disability (mild, moderate, severe, profound).

Conclusions: The W-ADL exceeded the recommended threshold for each quality criterion the authors evaluated. This freely available tool is an efficient measure of activities of daily living for surveys and epidemiological research concerning adolescents and adults with developmental disabilities.