Year	% of total
1990	20.18414573058243
1991	21.386868827998367
1992	21.72673226099879
1993	23.391074338606153
1994	25.3813032307751
1995	26.284609399487863
1996	27.97452270433343
1997	31.013108458418113
1998	31.718169547650067
1999	31.614715199486987
2000	31.80614035803985
2001	33.14901081418611
2002	33.670778339922386
2003	36.82943747591614
2004	38.61608503021006
2005	39.06089715651984
2006	38.70830743395288
2007	39.29991781479574
2008	38.45051978133407