Year	% of total
1990	24.588650247414286
1991	24.724299101436163
1992	24.849424519749135
1993	25.136900145409832
1994	25.221115005943496
1995	25.49641032262776
1996	25.659284781297753
1997	26.98247789894873
1998	27.24373952115071
1999	27.3215681046702
2000	27.95616166276923
2001	29.235802882533303
2002	30.46279992849637
2003	31.86424993045261
2004	32.852857409672346
2005	33.94255884790036
2006	35.57814323672743
2007	37.3154640472668
2008	38.4828520371633