The actometer: an evaluation of instrument applicability for chronic pain patients.

Three experiments were conducted to determine the reliability and validity of an activity measurement device, the actometer, as an index of ambulation for chronic pain patients. In experiment I, correlations between yoked actometers during ambulation showed the instrument to be internally reliable. In experiment II, actometer readings covaried very strongly with distance, showing the device to be valid during single trial assessment. However, experiment III found the device to show poor reliability over time (i.e., substantial measurement variability for the identical distance on 3 separate days). The results suggest that, for the chronic pain population, the actometer may not be a useful instrument for reliably assessing changes in walking activity over time.