Equating rehabilitation outcome scales: developing common metrics

Transparency with regard to measuring devices is one of the fundamental requirements for progress in science. The ability to derive comparable measures from different measuring devices is the cornerstone of transparency. To this end, progress in measuring and understanding rehabilitation outcomes requires that there is a method of measuring outcomes that is independent of the particular collection of items that is used to assess the outcomes. The purpose of this study is to develop a equivalence between the PECS Motor Skills and Cognition and Communication LifeScales with the FIM Motor Skills and Cognitive items. However, only the results of the Motor Skills Scale are reported here in the interest of brevity. This equating is based on approximately 500 simultaneous evaluations using bout the PECS and FIM scales on admission and discharge. The patients in this study were consecutive admissions to a free-standing rehabilitation hospital in early 1998. Patients from five diagnostic groups were included in this study, Brain Injury, Spinal Cord Injury, Stroke, Neuromuscular, and Musculoskeletal. The results indicate that it is possible to construct a common equal interval translation between the PECS and FIM for the two scales. Measures on the common metric can be based to either scale and are independent of the number of items completed. This use of these anchored scales will allow institutions using either the PECS and FIM to make direct comparisons of clinical outcomes with other institutions, independent of the particular outcome tool used to evaluate patients.