Year	% of total
1990	22.736446456101476
1991	23.0030112683749
1992	23.173836286633335
1993	23.443978847223377
1994	23.464979464207477
1995	23.87355376459443
1996	24.893761861566183
1997	25.413422031076276
1998	25.27198302226533
1999	25.686626057351678
2000	26.371328572920415
2001	27.684442003967966
2002	27.24765003832971
2003	27.9258219916087
2004	28.536795974736904
2005	28.476953154408932
2006	28.92865115925851
2007	28.536706085803846
2008	28.4852742480334