SELINSGROVE -- If you're going to lay some money down on this weekend's NFL playoff games, you might want to stay away from the over/under line according to a recent study which a Susquehanna University professor was part of.
"The Determinants of Scoring in 2010 NFL Games and the Over/Under Line" proved that bookmakers tend to set the over/under lines -- how many points the bookmaker expects the teams to combine for -- by giving a lot of weight on how many points the teams scored the previous week. But the study showed previous output has little impact on future results when it comes to scoring points.
That's what three researchers found when they analyzed over/under lines and the results of more than 190 NFL games played last season and the impacts of several variables used to set the betting line.
"Bettors place too much emphasis on recent information," says Tracy D. Rishel, associate professor of management at Susquehanna University.
Rishel, and two economists from Randolph Macon College -- C. Barry Pfitzner and Steven D. Lang -- presented their results at the annual meeting of the Southeast Institute for Operations Research and Management Sciences last fall.
Rishel, a Steelers fan, said she and the pair of Randolph Macon professors did the study to find a method "that put the focus on how teams matched up."
"We all follow sports and the sports betting literature is replete with naive betting rules," she continued. "'Bet the home 'dog; bet the team that has failed to cover the spread the last two times,' and stuff like that."
Rishel said by realizing that bookmakers emphasized points scored in the previous game, they could beat the over/under line up to 60 percent of the time. "Generally you must beat any bookmaker line by more than 52.4 percent to be profitable."
Another element that proved important in predicting where odds makers would set the over/under line was whether the game was played in a domed stadium with the roof closed. The dome factor, however, was not significant in predicting the number of actual points scored in the 2010 season, although a statistically significant relationship was found for the 2008 season.
"The dome effect may have captured the effect of teams that played in home domed stadiums and were also high-scoring teams for the 2008 season, but were not quite so productive in 2010," said Rishel.
The researchers also found that matchups on the field, one team's offense versus the opponent's defense, also played a role in setting the line, but to a lesser degree.
"Matchups count," notes Rishel. "Examination of yards gained on offense matched against yards surrendered on defense was highly statistically significant in the placement of the betting line."
The work by Rishel, Pfitzner and Lang -- which Rishel said took about a half-hour each week to record the data and a few days for the statistical work -- could be a cautionary tale for football bettors.
"The line, as expected, is much easier to predict than the actual points scored," says Rishel. "The outcomes and points scored are not easily predicted, which is 'why they play the games.'"