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)