Frances Woolley is a professor of economics at Carleton University. Andrew Kelly is an economics student at Carleton
University of Chicago economist Tobias Moskowitz and Sports Illustrated writer Jon Wertheim stirred up some controversy last year by claiming, in their book Scorecasting , that home team advantage is primarily due to officiating bias. “Home teams in hockey,” they argue, “get 20 per cent fewer penalties called on them and receive fewer minutes in the box per penalty.”
According to Moskowitz and Wertheim, referees are not consciously biased. Yet they are human and, “When humans are faced with enormous pressure – say, making a crucial call with a rabid crowd yelling, taunting and chanting a few feet away – it is natural to want to alleviate that pressure. By making snap-judgment calls in favor of the home team, referees, whether they consciously appreciate it or not, are relieving some of that stress.”
The Winnipeg Jets/Atlanta Thrashers offer a unique opportunity to test Moskowitz and Wertheim’s theories. Officials should face more pressure at the MTS Centre, packed full of Jets fans, than they did in the Philips Arena. If the authors are right, Winnipeg’s surprisingly strong home record this season should be due to, in part, to more favourable refereeing.
To put the theory to the test, we compiled home and away penalty statistics for the 2010/11 Atlanta Thrashers and the 2011/12 Winnipeg Jets. We focused on minor penalties only, because Moskowitz and Wertheim argue that the pro-home team bias should be particularly pronounced for less clear-cut calls, such as hooking or holding. Also majors are relatively rare – the Jets had only six this season, Atlanta had nine last year.
In 2010/11, Atlanta received 7 per cent fewer minor penalties than their opponents at home. This is in line with Moskowitz and Wertheim’s predictions, but it is hard to believe that Atlanta’s penalty advantage was due to some sub-conscious response to the taunts of Thrashers’ fans. The advantages any home team enjoys – to match lines, for example – could have caused them to take fewer penalties. Alternatively, the Thrashers' penalty advantage in home games might have been due to something about their game. Atlanta actually received fewer penalties than their opponents in away games, which is consistent with this idea.
In 2011/12, the Jets had the advantage of noisy fans amplified by the MTS Centre’s distinctive acoustics. Looking only at home penalty numbers, it would appear that fan support made little difference to the officiating: Winnipeg received just 2 per cent fewer minor penalties than their opponents in home games this season. This could be taken as evidence that the referees are immune to crowd pressure - or that the publication of Scorecasting, by making people aware of officiating bias, has helped to reduce or eliminate it.
Yet once Winnipeg’s home record is put into broader perspective, a slightly different pattern appears. Winnipeg had a penalty problem this year. In away games, they received 29 per cent more penalties than their opposition. It is possible that only fan pressure prevented the Jets’ home penalty record from being worse than it was.
The Jets/Thrashers comparison is a “natural experiment”. The 2011/12 Jets and the 2010/11 Thrashers had the same Southeast division opponents, and similar line-ups. The difference between the two teams should be due to something that changed when the Thrashers moved to Winnipeg. Fan support is one possibility. Another one, noted by many commentators, is travel schedules – Winnipeg had long stretches of home games, and the other teams in the Southeast division had to travel more. Certainly there was something other than officiating driving the Jets' home team performance this year. For example, Winnipeg had a 22 per cent powerplay efficiency at home this year, and third worst on the road, 12.7 per cent. Favourable calls are no use unless a team is able to capitalize on them.
The Jets/Thrashers experiment provides only limited support for Moskowitz and Wertheim’s hypothesis. But there is one thing they get right: “for shootouts - held during clearly important times in the game when you’d expect the crowd to be especially involved and boisterous - the significant home ice advantage normally present in the NHL evaporates.” The Jets’ shootout record was zero for three at home, three wins in four shootouts on the road.Report Typo/Error