Year	% of total
1990	12.179530921357216
1991	12.472095488779539
1992	12.619517706775362
1993	12.807467017694897
1994	12.90422415483852
1995	13.071808919436949
1996	13.83252905415221
1997	14.383140360150566
1998	14.598360966232875
1999	14.943649621501475
2000	15.397450148411064
2001	16.44159118617328
2002	16.877326768979547
2003	17.318414717810356
2004	18.012648645289364
2005	18.341599588867027
2006	19.172494885623156
2007	19.580772515688132
2008	20.00414412740442