NBA Referee Bias: Do Statistics Suggest a Home Court Advantage? Is there Favoritism toward Teams Facing Elimination?

In the summer of 2007, former National Basketball Association (NBA) referee Tim Donaghy was found to have bet on games that he officiated. Donaghy subsequently alleged that referee bias is rampant throughout the league. The scandal created widespread speculation about the legitimacy of controversial games in recent history, though NBA Commissioner David Stern argued vehemently that Donaghy was an isolated individual in his deviance. In light of this contentious issue, this paper empirically investigates whether there is evidence of referee bias. Specifically, home bias and prolonged playoff series bias are examined through analysis of multiple statistical categories, including discretionary turnovers (DTOs) and non-discretionary turnovers (NTOs). To analyze prolon ged series bias, this study observes teams facing elimination (down 2-3, 1-3, or 0-3) as well as those threatening to eliminate (up 3-2, 3-1, or 3-0). In these “one-sided elimination games,” or “pre-game 7 elimination games,” only a win by the team trailing in the series can extend the series to an additional game, generating added league revenue from ticket and advertisement sales. So, if the data analysis suggests that particular statistics are significantly favored toward teams facing “one-sided elimination,” it may suggest prolonged series bias among referees.

2007年夏季，前美国职业篮球联赛（National Basketball Association，以下简称NBA）裁判蒂姆·多纳吉（Tim Donaghy）被查出曾在自己执裁的赛事中参与赌球。多纳吉随即指控联盟内部裁判偏见问题猖獗。此次丑闻引发了公众对近年争议赛事合法性的广泛猜测，尽管NBA总裁大卫·斯特恩（David Stern）极力辩称，多纳吉仅是一名行为失范的孤立个体。针对这一颇具争议的议题，本文通过实证分析，探究是否存在裁判偏见的相关证据。具体而言，本文通过对多项统计维度的分析，检验主场偏见（home bias）与季后赛系列赛持久偏见（prolonged playoff series bias）是否存在，其中统计维度包括可裁量失误（discretionary turnovers, DTOs）与不可裁量失误（non-discretionary turnovers, NTOs）。为分析季后赛系列赛持久偏见，本研究选取了处于淘汰边缘的球队（系列赛比分落后2-3、1-3或0-3）以及手握赛点的球队（系列赛比分领先3-2、3-1或3-0）作为观测对象。此类‘单边淘汰赛事’（或称‘第7场赛前淘汰赛’）中，唯有系列赛落后方获胜才能将系列赛延长至下一场，进而为联盟带来门票及广告销售的额外营收。因此，若数据分析显示特定统计数据显著偏向处于淘汰边缘的球队，则可佐证裁判存在季后赛系列赛持久偏见。