Background Since clients with different types of developmental disabilities often experience difficulties in activities of daily living (ADL), it is critical that assessments of ADL are evaluated in order to ensure that one can make valid judgements based on the results of the appraisal. The purpose of the present study was to evaluate the validity of a specific performance assessment instrument, the Assessment of Motor and Process Skills (AMPS), when used by occupational therapists with clients with developmental disabilities. Unlike global ADL assessments, the AMPS is used not only to evaluate the level of ADL dependence, but also to estimate the quality of each specific action performed when a person is performing ADL tasks. Methods Data were gathered from 1724 participants with different developmental disabilities, including intellectual disability (ID), cerebral palsy and spina bifida. Many-Facet Rasch (MFR) analysis was used to examine person-response validity, and task and item scale validity. Results Goodness-of-fit statistics showed that the tasks and items had acceptable scale validity. The participants had acceptable person-response validity on the ADL motor scale, but had slightly lower than expected levels of person-response validity on the ADL process scale. The results indicate that clients with more severe forms of ID may have a higher proportion of different performance profiles in ADL than is expected by the MFR model of the AMPS. Since the proportion of participants who did not meet the criteria was only 3% lower than expected and in accordance with other studies, the difference may not be clinically meaningful. Otherwise, the results indicated that the AMPS is a valid tool when used with clients with developmental disabilities. Conclusions Further research is needed to evaluate the use of the AMPS in clinical assessment and intervention planning for this group of clients.
