The authors develop a model to investigate potential biases of inherent characteristics in betting markets. The test requires only that there be both a sides (‘‘spread’’) market and a totals (‘‘over/under’’) market for the game. The authors utilize the model to test for the well-documented ‘‘home-underdog’’ bias in the National Football League (NFL). They show that the bias specifically favors the offense (or defense) of home underdogs (away-favorites), with no bias against the offense (defense) of away favorites (home-underdogs).
We test the NBA betting market for efficiency and find that totals lines are significantly biased early each season, yet sides lines do not show a similar bias. While market participants generally force line movements in the correct direction from open to close, they do not fully remove the identified bias in totals lines. This inefficiency enables a profitable technical trading strategy, as the resulting win rate of our proposed simple betting strategy against the closing totals line is 56.72%.