Table 1 Sample sizes in each category for the four groups, season of collection dates, and period for which players were considered. Date Group Category Sample Total 2005-2006 (Born 1986-1994) Elite 1 Under 11 110 834 Under 13 184 Under 15 234 Under 18 306 2008-2009 (Born 1989-1997) Elite 2 Under 11 546 2768 Under 13 686 Under 15 644 Under 18 892 Amateurs Under 11 163 591 2006-2007 Under 13 169 (Born 1988-1996) Under 15 145 Under 18 114 2008-2009 Spanish population 4738110 (Born 1986 - 1997)