Commentary on measuring disability.

This is a commentary on 5 articles in this issue of Archives of Physical Medicine and Rehabilitation that report on several related studies of new approaches to measuring disability. The project was grounded in theory, beginning with the development of a conceptual framework enhanced by a literature review and expert consultation within and outside of the Social Security Administration. The investigators then used item response theory to develop test items, which they organized into computer adaptive testing instruments and tested them for their psychometric properties. All in all, it is a groundbreaking set of studies and an enormously valuable contribution to the field. Hopefully it will also be tested as an alternative approach to assessing disability in the Social Security Administration disability benefits programs.