Reliability of tremor measurements using a multidimensional electromagnetic sensor system

Objective: To investigate the reliability of repeated measurements of norma l physiological tremor made with a multidimensional measurement system. Equipment: Measurements of postural upper limb tremor at the hand were made in 10 normal subjects using a 3Space Fastrak(R) (Polhemus, Inc.) which det ects movement over six degrees-of-freedom (three of the measurement directi ons were examined). Data collection: Reliability was assessed for two alternative upper limb po stures (arm straight or bent) and data were collected on two days, twice at each session, to determine the repeatability between and within recording sessions. Data analysis: The data were split into segments and subjected to autoregre ssive (AR) modelling. Three parameters (one for each of the measurement dir ections examined) were extracted from the models and used as variables for the reliability analysis. Statistical tests: Variation within and between sessions was assessed by fi nding the median differences between efforts and days for each subject and then finding the overall median value and the corresponding 97.9% confidenc e intervals for each movement. This produced estimates of the population me dian value and indicated the precision of the estimates. Results: All the confidence intervals encompassed the zero median differenc e point indicating that, in the population, this technique would produce re peatable results. For between-efforts comparisons there was some evidence t hat data collected for the bent arm posture were more repeatable than for a straight arm. Conclusion: Normal physiological tremor can be measured reliably, within an d between sessions, using the 3Space Fastrak system.