Let Them Be the Judge of That: Bias Cascade in Elite Dressage Judging.

Sport performances judged subjectively often suffer from systematic errors due to biases, with the sport of equestrian dressage being no exception. This study examines whether international dressage judges display systematic errors while evaluating elite horse-rider combinations. Data from seven 5* Grand Prix dressage events between May 2022 and April 2023 were analyzed (510 judges' scores) using Multivariable Linear Regression Analysis. Five predictor variables-Home, Same Nationality, Compatriot, FEI Ranking and Starting Order-were studied in relation to Total Dressage Score (TS). The model accounted for 44.1% of TS variance; FEI Ranking, Starting Order, Compatriot, Same Nationality, and Home were statistically significant ( p < 0.001). Judges exhibited nationalistic and patriotism-by-proxy biases, awarding significantly higher scores to riders from their countries ( p < 0.001). FEI Ranking and Starting Order also influenced scores significantly ( p < 0.001). These biases, combined, created a cascade effect benefiting a specific group of riders. To address this, measures should be taken to develop a more objective judging system that is based on unequivocal, transparent and evidence-based criteria and supports the continuous development of a fair, sustainable, equine welfare orientated sport that fosters societal acceptance.