THE APPLICATION OF GENERALIZABILITY THEORY TO RELIABILITY ASSESSMENT - AN ILLUSTRATION USING ISOMETRIC FORCE MEASUREMENTS

Background and Purpose. The objective of this study was to examine the potential use of the generalizability theory for assessing reliabilit y of muscle force measurements in clinical applications. Reliability i s expressed in terms of standard error of measurement (SEM) and the in dexes derived from the SEM Using generalizability theory, potential so urces of measurement error can be recognized and estimated. Subjects. Ten healthy women, aged 23 to 47 years (XBAR = 29.5, SD = 7. 1), parti cipated in the study. Methods. The method is illustrated by presenting a pilot study. Repeated measurements of maximal isometric knee extens ion force were carried out by two therapists. The time interval betwee n measurement occasions was 1 week. A functional prototype of a hand-h eld dynamometer was used, and measurements were carried out according to standardized test protocols. Results. Relatively important sources of measurement error were associated with interaction effects between subject and therapist as well as with interactions including the facto r occasion. The SEM of the net knee moment was estimated for various h ypothetical applications of the dynamometer. Conclusion and Discussion . It is concluded that the SEM, the corresponding confidence interval, and the smallest detectable difference are practical measures for exp ressing reliability of measurements on an individual. Generalizability theory is a powerful tool for estimating the magnitude of multiple so urces of measurement error and for assessing the reliability of measur ements tailored to specific clinical applications.