Referees home bias before and after challenge system: the case study of international volleyball league

This empirical study intends to shed some light on the sport that is received little attention from academics study which is international volleyball league. Since 2013, FIVB adopts Challenge System in which coach and player are able to request for video review to recheck referees’ decision. Motivated by this new technology, this study sets upon 3 main objectives: to investigate the existence of home biased, to investigate change in referee’s behavior after the Challenge System was introduced, and to examine whether one biased decision could affect the probability of wining the next point. Each observation is manually collected from video review. Logit regression is used to estimate the probability of making incorrect and disputable point, and the probability of winning the next point. Differences in Differences model is used to capture change in referee’s behavior. The empirical results show that referee is biased in favor home team but monitoring pressure from challenge system reduces referee bias. Also, there is an empirical evidence shows that team is more likely to win the next point after being awarded an incorrect of disputable point. However, this study found that crowd pressure decreases probability of making disputable and incorrect decision.

本实证研究旨在探讨学界关注度较低的赛事领域——国际排球联赛（International Volleyball League）。自2013年起，国际排联（FIVB）引入挑战系统（Challenge System），允许教练与球员申请视频回放以复核裁判判罚。受此项新技术的启发，本研究确立了三大核心研究目标：一是探究主场偏见（home bias）的存在性；二是考察挑战系统引入后裁判判罚行为的变化；三是检验单次有偏判罚是否会影响后续一分的获胜概率。所有观测数据均通过视频回放人工采集得到。本研究采用逻辑回归（Logit Regression）模型，分别估计出现错误判罚与争议判罚的概率，以及后续一分的获胜概率；同时采用双重差分（Differences in Differences, DID）模型捕捉裁判判罚行为的变化。实证结果表明，裁判存在偏袒主场球队的倾向，但挑战系统带来的监督压力能够有效削弱裁判偏见。此外，实证证据显示，球队在获得错误或争议判罚的利好后，更有可能赢下后续一分。但本研究同时发现，观众压力会降低裁判作出错误或争议判罚的概率。