Umpires may be playing favourites on the field, according to a new study co-authored by McGill University.

Research show umpires monitoring Major League Baseball games are more likely to make calls in favour of the pitcher if they share the same race or ethnic background.

More than 2 million pitches over three seasons of MLB games were analyzed during the study by Christopher Parsons, an assistant professor of finance at McGill's Desautels Faculty of Management. His colleagues at the University of Texas and Auburn University co-authored the study.

According to their research, there is about a 32 per cent chance an umpire will call a pitch a strike. However, if the umpire happens to be of the same race or ethnicity then the percentage increases by about one per cent.

The study found the likelihood of a racial bias was even greater at games where umpires were not being closely monitored.

"This effect is magnified in situations where there is comparatively little scrutiny on the umpire -- in stadiums that are not equipped with computerized monitoring systems; at poorly attended ballgames; and on pitches unlikely to determine the outcomes of individual at-bats," McGill University said in a statement.

"Because baseball is such a close game, a pitch here and there can have a great influence on the outcome of a single game," said Parsons on the impact of an umpire's calls.

The study goes further by looking at pitchers' salaries.

Umpires call about 75 pitches for each team during a typical game. Throughout the season, they call about 400,000 pitches.

"Umpires judge the performance of players every game, deciding whether pitches are strikes or balls," Daniel Hamermesh, the Edward Everett Hale Centennial Professor of Economics at the University of Texas at Austin.

"Discrimination affects the outcome of a game and the labour market, determining the pitcher's market value and compensation," Hamermesh said in a statement.

The results are also troubling from an economics perspective, Hamermesh said.

"Because if workers are discriminated against when their performance is evaluated, then the ability to detect discrimination in other areas is reduced," he said.

The research concludes that because a pitcher's salary is negotiated based on his success on the field, and because close to 90 per cent of umpires are Caucasian, then pitchers who are a minority are also at an economic disadvantage.

During the study, which took place between 2004 and 2006, most ballparks didn't have the monitoring systems that are in place now, Parsons said.

Nonetheless, he suggested the MLB association take steps to mix things up on the field by changing the race ratio between pitchers and umpires to avoid any opportunity for bias.