An Evaluation of the Measurement Properties of An Activities of Daily Living Scale for Adults with Autism, Down Syndrome, Fragile X, and Other Intellectual Disabilities

Background:

Adults with autism experience a wide range of difficulties in performing daily activities; some might encounter severe limitations in self-care and basic tasks necessary for independent living, while others have few limitations in these areas. Activities of Daily Living (ADLs) are considered durable indicators of “activity limitations”—consistent with the World Health Organization’s dimensional framework for disability. ADL instruments have been used extensively in clinical applications, research, and public health practice.  However, there is a paucity of freely-available and high quality tools for measuring activity limitations among adults with autism or other developmental disabilities.

Objectives:

To describe the development of the Waisman Activities of Daily Living (W-ADL) Scale, and to thoroughly evaluate its measurement properties for adults with developmental disabilities.

Methods:

This analysis utilized four well-characterized and longitudinally-studied groups of adults with developmental disabilities: 406 adults with autism; 147 adolescents and adults with fragile-X syndrome; 169 adults with Down syndrome, and 292 adults with intellectual disability (but not Down syndrome). The W-ADL Scale consists of 17 items that pertain to the target adult’s current performance in daily activities such as grooming, bathing, running errands, and preparing meals. The target adult’s performance of each activity is rated on a 3-point scale (0=“does not do at all”, 1=“does with help”, 2=“independent”), and item scores are summed to produce an overall score. W-ADL items were administered at the beginning of each study. Items were readministered at three additional time points for adults with autism and seven additional time points for adults with Down syndrome or intellectual disability.  We evaluated the W-ADL according to an established set of quality criteria for the measurement properties of health status questionnaires (Terwee et al, 2007).

Results:

Cronbach’s alphas for the W-ADL ranged from 0.88 to 0.94 in the four disability groups, and a single-factor structure was most parsimonious.  Comparisons of consecutive time points resulted in weighted kappas between 0.92 and 0.93, suggesting high reliability. Construct validity was supported through substantial associations between the W-ADL and the level of employment or participation in educational programs, maternally-reported need for respite services, maternal caregiving burden, and target adult IQ. Criterion validity was demonstrated with a correlation of 0.78 between the W-ADL and Vineland Screener standard score among adults with autism.  The W-ADL demonstrated no floor or ceiling effects in any of the four groups. Among adults with Down syndrome and intellectual disability, there were significant group differences in W-ADL scores by subjective maternal ratings of “mild”, “moderate”, “severe”, and “profound” intellectual disability. We estimate that a 1-point change in W-ADL scores is detectable in samples of at least 35 people.

Conclusions:

The W-ADL exceeded the recommended threshold for each quality criterion we evaluated, and appears to have desirable measurement properties as a research instrument. Additional work is needed to evaluate its utility and applicability in different cultures and contexts.  This freely-available tool has practical applications as an efficient measure of activities of daily living for research concerning adults with autism and developmental disabilities.