ONLY CHALLENGE "OUT" CALLS

Two tennis players are locked in a furious baseline exchange. Eventually, a line judge calls the ball "out." Should the player who lost the point protest the ruling?

Yes, a new study suggests. Researchers say professional tennis players could increase their chances of having a ruling reversed in their favor by an instant replay review if they challenge "out" calls more than "in" calls.

A study of 57 randomly selected matches during the 2007 Wimbledon tournament found that officials were more likely to err by calling a shot "out" than "in." It's not a matter of bad refereeing, scientists say, but rather, it has to do with a bias in the way humans perceive moving objects.

"When a ball is called 'in,' a player should usually not challenge the call, even when she believes it to be an incorrect call," psychologist David Whitney of the University of California, Davis wrote in the study. "Players should concentrate their challenges on balls that are called 'out."'

In the study, three scientists independently reviewed TV footage of 4,457 points from Wimbledon in 2007. Calls were spot on most of the time. Of the 83 wrong rulings, researchers found, 70 -- or 84 percent -- were instances of a shot landing in but being called "out." Only in 13 cases was a ball that landed out ruled "in."

Researchers attributed the errors to perceptual bias in which a moving target appears to be farther along its path than it really is -- a bias phenomenon also seen in the general population.

AP