Inter-Unit Reliability and Effect of Data Processing Methods of Global Positioning Systems.

PURPOSE: To establish the inter-unit reliability of a range of Global Positioning System (GPS)-derived movement indicators, determine the variation between manufacturers, and investigate the difference between software-derived and raw data.

METHODS: A range of movement variables were obtained from 27 GPS units from three manufacturers (GPSports EVO; 10 Hz, n = 10: STATSports Apex; 10 Hz, n = 10: and Catapult S5; 10 Hz, n = 7) that measured the same team-sports simulation session while positioned on a sled. The inter-unit reliability was determined using the coefficient of variation (CV; %) and 90% confidence limits (CL), whereas between manufacturer comparisons, and also comparisons of software versus raw processed data were established using standardized effect sizes (ES) and 90% CL.

RESULTS: The inter-unit reliability for both software and raw processed data ranged from good to poor (CV = 0.2%; ±1.5% to 78.2%; ±1.5%), with distance, speed, and maximal speed exhibiting the best reliability. There were substantial differences between manufacturers, particularly for threshold-based acceleration and deceleration variables (ES; ±90% CL [-2.0%; ±0.1 to 1.9%; ±0.1%]), and there were substantial differences between data processing methods for a range of movement indicators.

CONCLUSIONS: The inter-unit reliability of most movement indicators were deemed as good regardless of processing method, suggesting that practitioners can have confidence within systems. Standardized data processing methods are recommended, due to the large differences between data outputs from various manufacturer-derived software.