Applying psychometric criteria to functional assessment in medical rehabilitation: I. Exploring unidimensionality.

While rehabilitation providers are facing increasing pressure to document treatment outcomes, critics have warned against the inappropriate use of ordinal functional assessment data in arithmetic operations. Two salient criticisms concern the combination of items representing multidimensional abilities into a single total score, and the indeterminate distances between hierarchical functional assessment scale categories. In this initial study, the factor structure of the Patient Evaluation and Conference System (PECS) was studied to assess the potential for unidimensional measurement. Factor analysis of a multidiagnostic dataset (n = 3,564) yielded eight factors accounting for 60% of the variance among 68 PECS items. The factors indicate that several unidimensional measures may underlie the PECS. These factors are delineated, and further studies of unidimensionality and additivity are recommended.