Year	% of total
1990	22.733946846813065
1991	23.000571709127378
1992	23.171442501415832
1993	23.441592084354035
1994	23.46264900761576
1995	23.87121007993212
1996	24.891356279853028
1997	25.410580955414872
1998	25.269220539313256
1999	25.683797623263274
2000	26.368454179403
2001	27.681436465724115
2002	27.244765380900027
2003	27.922585481670673
2004	28.53355977656176
2005	28.473844104644378
2006	28.925484236645985
2007	28.53368364999296
2008	28.48233246620262