An application of generalizability theory to study a physical performance measure in Parkinson's disease

Clinicians and researchers frequently quantify impairments and functional a bility to monitor patient's symptoms and progress. For some patients, such as those with Parkinson's disease (PD), symptoms can fluctuate from day to day, making reliable measurement difficult. Multiple measures then may be r equired to obtain reliable data. Decisions must be made, balancing the opti mum measurement schedule to obtain "good reliability" against burden to the patient. This investigation demonstrates the use of Generalizability Theor y in determining the testing schedule when designing an experiment involvin g patients with known fluctuations of symptoms. In this investigation we us e "Functional Axial Rotation" (FAR), a measure of spinal flexibility, to il lustrate the use of Generalizability Theory for designing an experiment usi ng participants who have PD. Measurements of FAR were taken on 13 participa nts, aged 60 or older, who were in early and mid-stages of PD. Three measur ements were obtained on each of two consecutive days, and repeated on two c onsecutive days a week later, giving a total of 12 measures of FAR for each individual. Four sources of variation (subject, week, day and trial) were employed to estimate the reliability of FAR under several designs. Assuming different schedules of measures across weeks, days and trials, the estimat ed reliability of FAR for four measurements is in the range of 0.75 to 0.83 , and for eight measurements in the range of 0.82 to 0.86. We discuss the u se of this type of analysis in the determination of the optimum measurement design for experiments involving subjects with known fluctuations. (Aging Clin. Exp. Res. 12: 29-34, 2000) (C)2000, Editrice Kurtis.