Year	% of total
1990	22.733946846813055
1991	23.000571709127367
1992	23.171442501415836
1993	23.441592084354035
1994	23.462649007615752
1995	23.871210079932123
1996	24.891356279853024
1997	25.41058095541488
1998	25.269220539313253
1999	25.68379762326327
2000	26.36845417940301
2001	27.681436465724108
2002	27.244765380900017
2003	27.922585481670684
2004	28.53355977656176
2005	28.473844104644368
2006	28.925484236645975
2007	28.533683649992962
2008	28.482332466202617