Previous research (Barnsley, Thompson, & Barnsley, 198S) demonstrated an extremely strong linear relationship between the month of birth (from January to December) and the likelihood of playing in the National Hockey League and two major developmental Junior hockey leagues. The present study analyzes the birthdates of 7313 hockey players participating in the Edmonton Minor Hockey Association in the 1983-1984 season. The main findings are that players possessing a relative age advantage, i.e., born in the months of January to June, are more likely to participate in minor hockey and are more likely to play for "top tier," or "rep" teams than are players who are born in the months of July to December and thereby are disadvantaged by their relative age. Proposals by which these relative age effects could be reduced are considered.

Recent studies indicate that month of birth is related to achievement in a number of sports. Birth dates were collected for all players on teams competing in the 1990 World Cup and the 1989 Under-17s and Under-20s World Tournaments in Football. Results indicated that those born early in the "activity year" (August 1 through July 31 for football) were over- represented, while those born later were under-represented. The effect was particularly strong in the Under-17s and Under-20s tournaments. Results are interpreted in the context of the "relative age effect".

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The records of 837 major league baseball players were examined in order to determine whether the Little League age eligibility criterion, based on the month of birth, affected participation rate at the professional level. The results indicated that major league players were more likely to have been born in the first months of the year, if that year corresponded to the one used for eligibility for Little League baseball (i.e., beginning in August and ending in July). A reanalysis of data presented in the literature (which suggested no effect) produced a similar result. These data are interpreted in terms of the relative age effect. That is, because of age cutoffs used in Little League baseball, some players gain a developmental advantage when competing against other youngsters who are considerably younger, although they are placed in the same age category for league play.

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