Assessment of the kinematic variability among 12 motion analysis laboratories.

Variability of kinematic measurements among sites participating in a collaborative research investigation is a primary factor in determining number of subjects, level of detectable difference and statistical power of a multi-site research study. In this study, one subject was evaluated by 24 examiners at 12 motion analysis laboratories and the observed variability of nine kinematic parameters are reported. Following implementation of a standardized gait analysis protocol the same subject returned for another evaluation at each of the 12 laboratories. Additionally, system accuracy and variability of the subject within and between test days are included as factors that may affect between site variability. Marker placement among examiners is identified as the largest source of variability. A 20% decrease in variability was noted following implementation of the standardized protocol.