Objective. The Assistive Technology Outcomes Profile for Mobility (ATOP/M), is designed to measure the specific functional effects of mobility assistive devices, such as canes, orthotics, walkers and wheelchairs, on performance of mobility-related activities and participation as defined in the International Classification of Functioning, Disability and Health (ICF) framework. This paper described the development of the instrument and discusses the approach taken to faithfully capture the perspectives of device users.

Materials and Methods. The first step in developing the instrument was to assemble an item pool. Extant instruments for measuring the functional areas from which items might be selected were reviewed and qualitative analysis of focus group discussions was performed. A pool of 148 items was created using items drawn from the Patient-Reported Outcomes Measurement Information System (PROMIS), the Community Participation Indicators (CPI, v. 4), and over a dozen other instruments. Nine focus groups were conducted in the USA and Canada with multiple stakeholder groups to identify additional items and to refine item wording and response format. The ATOP/M pool was field tested in a survey of 1,037 mobility device users to calibrate items. Rasch analyses were done to create full-length and short form instruments and an item bank for computer adaptive testing (CAT) applications.

Results. The full-length ATOP/M consists of 68 items distributed across two domains, each having two subdomains: Activities (Physical Performance and Instrumental Activities of Daily Living); Participation (Social Role Performance and Discretionary Social Participation). It yields two scores, one reflecting respondents' mobility level while using a device, the other reflecting their capability without it. All item banks had acceptable reliability, were essentially unidimensional, and had acceptable model fit for most items. Validity evidence was found in significant differences for persons using canes or scooters versus those using manual or power wheelchairs. Some of the items proposed by the focus groups did not survive the psychometric analyses. These items concerned the effect of devices on helping people to manage their disability.

Conclusions: The ATOP/M comprises items that reflect the self-assessed performance of activities and participation in areas that are important to users of mobility assistive devices. The instrument has excellent person and item reliability, and no significant ceiling and floor effects. The ATOP/M has been translated into Canadian-French, and its validity is receiving further examination in several Canadian studies. The instrument development revealed that end-users have some expectations of mobility devices impact that are not easily measured. Assistive technology outcome assessment should consider approaches that combine questionnaires with other methods for obtaining end-user perspectives.

Acknowledgments. This study was funded in part by the National Institute on Disability and Rehabilitation Research Grant #H133A060062 through the Consortium for Assistive Technology Outcomes Research (CATOR).