This paper presents empirical tests of market rationality using data from the point spread betting market on National Football League games. Data from this market avoid many common pitfalls of tests of rationality in conventional financial markets. The authors test for rationality with two types of tests, statistical and economic. Results of the tests reveal that the statistical tests cannot reject market rationality while the economic tests do reject market rationality.

ABSTRACT This paper presents empirical evidence comparing two models of trading in equities—the well‐known tax‐loss‐selling hypothesis and “the disposition effect.” According to the disposition effect, investors are reluctant to realize losses but are eager to realize gains. This paper distinguishes between the two models with a new methodology that examines the relationship between volume at a given point in time and volume that took place in the past at different stock prices. The evidence overwhelmingly supports the disposition effect not only as a determinant of year‐end volume, but also as a determinant of volume levels throughout the year.