Effect of a Change in Selection Year on Success in Male Soccer Players WERNER F. HELSEN, 1 * JANET L. STARKES, 2 AND JAN VAN WINCKEL 1 1 Department of Kinesiology, Katholieke Universiteit Leuven, Leuven, Belgium 2 Department of Kinesiology, McMaster University, Hamilton, Canada ABSTRACT Since 1997 and following the guidelines of the International Football Association, the Belgian Soccer Federation has used January 1st as the start of the selection year. Previously, August 1 was the start. This shift prompted an investigation of changes in birth-date distributions throughout youth categories for 1996–1997 compared to the 1997–1998 com- petitive years. Birth dates were considered for national youth league players, ages 10–12, 12–14, 14–16, and 16–18 years. Kolmogorov Smirnov tests as- sessed differences between observed and expected birth-date distributions. Regression analyses examined the relationship between month of birth and number of participants both before and after the August to January shift. Results indicated that from 1996 to 1997, youth players born from January to March (the early part of the new selection year) were more likely to be iden- tified as “talented” and to be exposed to higher levels of coaching. In com- parison, players born late in the new selection year (August to October) were assessed as “talented” in significantly lower proportions. Specific suggestions are presented to reduce the relative age effect. Am. J. Hum. Biol. 12:729–735, 2000. © 2000 Wiley-Liss, Inc. There has been a long-standing tradition in human biology research of studying the relationship between seasonal variation and biological aspects of human develop- ment (e.g., Malina and Himes, 1977; Shep- hard et al., 1978, 1979). New insights re- lated to month of birth have been reported for human growth. For example, Weber et al. (1998) have recently found a dependence of height at 18 years of age on birth month. Over 10 years, the authors showed a clear sinusoidal cycle with maximum variation in spring and minimum variation in autumn, and average differences of 0.6 cm. Given that height is significantly influ- enced by month of birth, it is not surprising that in sports, where advanced physical de- velopment may be advantageous, research- ers have demonstrated a consistent asym- metry in the birth-date distribution of professional players. For example, Barnsley et al. (1985) demonstrated a strong linear relationship between month of birth (Janu- ary to December) and the proportion of play- ers in the National Hockey League and two of Canada’s main “Junior A” professional ice hockey development leagues. In all of these leagues, approximately four times more players were born in the first quarter of the “hockey year” than were born in the last quarter. More recently, it has been shown that similar asymmetries in birth-date dis- tributions are also apparent in several other professional sports (for a review, see Boucher and Mutimer, 1994). These findings in senior players have led a number of investigators to examine whether similar asymmetries emerge throughout youth sport categories. To pro- vide developmentally appropriate training, competition, and equal opportunity for suc- cess, children are grouped by chronological *Correspondence to: Werner Helsen, Katholieke Universiteit Leuven, Motor Learning Laboratory, Tervuursevest 101, 3001 Leuven, Belgium. E-mail: werner.helsen@flok.kuleuven.ac.be Received 22 May 1998; Revision received 31 December 1999; Accepted 7 January 2000 AMERICAN JOURNAL OF HUMAN BIOLOGY 12:729–735 (2000) © 2000 Wiley-Liss, Inc. PROD #M98042R3