Parents worried about whether their child has the goods to make it into the NHL might now have another seemingly arbitrary factor working against them ? the time of year their hockey prodigy was born.

A study, published Wednesday in the online science journal PLOS ONE, suggests that the NHL is guilty of an age bias because it weighs its draft selections more heavily in favour of players born earlier in the year.

The report found that 36 per cent of players drafted by NHL teams between 1980 and 2007 were born in the first quarter of those years, or from January to March, compared to 14.5 per cent of draftees who were born in the fourth quarter.

Rob Deaner, one of the study's authors, said it has been widely known that a so-called selection bias exists in various sports and educational pursuits, but it hasn't been demonstrated before in the NHL.

"It's never been shown that people are systematically underestimating the ability of the younger players," said Deaner, an associate professor of psychology at the Grand Valley State University in Michigan.

"We found the teams are consistently underestimating how good the guys are that are born from July to December."

The authors looked at about 2,700 Canadian players drafted by NHL teams over a 27-year period, finding that those born in the third and fourth quarters were drafted more than 40 slots later than their productivity warranted.

Deaner said the selection bias can start at an early age, when a 12-year-old player born between January and March will be streamed into an elite level of hockey, ahead of his peers born later in the year.

He said younger players may be just as good, but might not be as big or as skilled and will likely end up in a lower league.

"On average, the players who are drafted in a lower league might turn out to be better and those players might more often be relatively younger," he said.

A spokesman for the NHL could not be reached for comment.

The authors contend that the strategy might actually work against a team's success because they found that players born later in the year and drafted later actually had more productive hockey careers.

Deaner said the study showed that men drafted in the second half of the year were about twice as likely to have successful careers in the NHL ??? reaching benchmarks like 400 games played or 200 points scored ??? than those born earlier in the year.

"If the team wasn't making this mistake, they probably would have been more successful," he said. "The guys born in the first part of the year are much more likely to be busts."