Year	Percent
1990	27.65
1991	28.28
1992	28.92
1993	29.55
1994	30.19
1995	30.82
1996	31.46
1997	32.09
1998	32.72
1999	33.36
2000	34.02
2001	34.18
2002	34.26
2003	34.37
2004	34.5
2005	34.63
2006	35.02
2007	35.4
2008	35.81
2009	36.21
2010	36.49
2011	36.57
2012	36.62
2013	36.68
2014	36.75
2015	36.82