sealPurdue News

December 9, 2002

Purdue prof says hockey rule changes miss the goal

WEST LAFAYETTE, Ind. – Two rule changes intended to add excitement to professional hockey have unintentionally changed the game's incentive structure and encouraged teams to play for ties, says a Purdue University economist.

Jason Abrevaya

Jason Abrevaya (ah-brah-VAY-ya), an associate professor of economics at the Krannert School of Management, does econometric research, which applies sophisticated mathematical and statistical tools to solve problems and test theories. He turned his tools loose on the National Hockey League, which enacted rule changes to make the game more exciting for fans by reducing the number of games that ended in ties.

"Generally speaking, American sports fans don't like ties," Abrevaya says. "After the game is played for two or three hours, they like to see a winner."

Among major sports, hockey is the only major professional sport in which ties pose a significant dilemma, Abrevaya writes. In the NHL, roughly one out of every seven regular-season games between the 1995-96 and 1998-99 seasons ended in a tie.

"Prior to the 1999-2000 season, the NHL awarded teams two points for a win, one point for a tie and zero points for a loss," Abrevaya says. "The total number of points accumulated by a team dictates final standings, making the playoffs and seeding."

Before the 1999-2000 season began, the league instituted two rule changes:

1. A team that loses in overtime receives one point.

2. Overtime is played with four, rather than five, skaters (plus the goalie).

"The rule changes had the intended effect of reducing the number of ties in overtime games," Abrevaya says. "Before the rule change, 71.1 percent of overtime games ended in ties. After the rule change, only 55.5 percent of overtime games ended in ties."

In econometric terms, the change is considered statistically significant.

There also was less willingness to settle for a tie and more aggressive play, with a 37.5 percent increase in shots on goal in overtime (5.46 shots on goal in overtime versus 3.97 shots on goal before the rule change).

Abrevaya says from a marketing point of view, this is good for the league.

"A sports league's main objective is to increase and maintain demand for its product by providing excitement and enjoyment to its fans."

The unintended consequence, though, was that there was a 12.1 percent increase (19.8 percent before the rule change and 22.2 percent with the new rules) in the number of overtime games.

"All else being equal, the potential for the available larger pie makes an overtime game an appealing outcome for teams," Abrevaya writes.

Abrevaya is most interested in the incentive effects of the changes for teams.

"There is a perverse incentive for teams to play to reach overtime," he says. "Had the likelihood of reaching overtime remained constant, a more desirable drop in the percentage (from 14.1 percent to 11 percent) of ties would have been achieved."

Abrevaya used the USA Today's online statistical archive of 7,821 regular-season NHL games played from the 1995-96 season through the 2001-02 season. He used a software program to put the data into a usable format and applied probability and regression techniques to come to his conclusions.

Writer: Mike Lillich, (765) 494-2077,

Source: Jason Abrevaya, (765) 496-2689,

Purdue News Service: (765) 494-2096;

Related Web site:
Full text of Jason Abrevaya's research paper


Fit to be tied: The incentive effects of overtime rules
in professional hockey

Jason Abrevaya

This paper examines the incentive effects of different payoff structures in the National Hockey League. A rule change prior to the 1999-2000 season, which changed the way that teams were awarded points in overtime games, provides a natural experiment to test the reaction of teams to a change in playoff structure. The rule change had the desired effect of increasing excitement during overtime play. However, this paper shows that the rule also had the effect of increasing the frequency of overtimes games, an effect predictable from the change in incentives but not one intended by the league.

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