Reliability in evaluating passive intervertebral motion.

Reliable measurements are prerequisite to the successful conduct of outcome studies. In a study of the performance of physical therapists (n = 5) in evaluating passive mobility of the vertebral column with normal subjects (n = 5), several sources of measurement variability were assessed: the reliability within and between therapists, the criteria for grading, and the subjects themselves. Intratherapist reliability was found to be dependable; intertherapist reliability was not. Problems that merit further study were identified as idiosyncratic behaviors that may develop with experience, subject characteristics, and the instrument itself. Periodic assessment of the reliability of therapists in performing evaluations is recommended because of its importance to therapeutic programming.