Reliability of spatial-temporal metrics used to assess collective behaviours in football: an in-silico experiment

Background The purpose of this study was to investigate the reliability of spatio-temporal measurements applied within collective behaviour research in football. Methods In silico experiments were conducted introducing positional errors (0.5, 2 and 4 m) representative of commercial tracking systems to match data from the 2020 European Championship qualifiers. Ratios of the natural variance ('signal') of spatio-temporal metrics obtained throughout sections of each game relative to the variance created by positional errors ('noise') were taken to calculate reliability. The effects of error magnitude and time of analysis (1, 5 and 15 mins; length of attack: <10, 10-20, >20 s) were assessed and compared using Cohen's f(2) effect size. Results Error magnitude was found to exert greater influence on reliability (f(2) = 0.15 to 0.81) compared with both standard time of analysis (f(2) = 0.03 to 0.08) and length of attacks (f(2) = 0.15 to 0.32). Discussion The results demonstrate that technologies generating positional errors of 0.5 m or less should be expected to produce spatio-temporal metrics with high reliability. However, technologies that generate errors of 2 m or greater may produce unreliable values, particularly when analyses are conducted over discrete events such as attacks, which although critical, are often short in duration.