Year	% of total
1990	22.19465903202262
1991	22.86282377203172
1992	23.077234386665012
1993	23.712743861904347
1994	23.626637843973892
1995	23.94651065936078
1996	24.675639365104903
1997	25.08987566171022
1998	25.229377324433845
1999	25.52534921699051
2000	26.339526541007025
2001	27.111391390745695
2002	26.979117306899475
2003	27.043575327488487
2004	26.96898361261995
2005	26.659157757415635
2006	26.910427484609468
2007	26.593055498244446
2008	26.629656766915183