The reliability and validity of two ambulatory monitoring actigraphs.

Evidence for the reliability and validity of two models of Ambulatory Monitoring, Inc. actigraphs was obtained by testing four instruments of each kind 10 times each on a precision pendulum. Correlation and coefficient of variation methods were used to analyze the data. Reliability coefficients of .98 were obtained for both models. Coefficient of variation methods yielded reliability coefficients of 92% for the MotionLogger model and 97% for the BuzzBee model. Validity coefficients of.99 were obtained for both models. However, MotionLogger means were found to differ by up to 36% from one instrument to another, whereas BuzzBee means differed by 10% at most. Issues of standardization and measurement units were discussed.