Year	Percent
1990	27.44
1991	27.71
1992	27.98
1993	28.24
1994	28.51
1995	28.78
1996	29.05
1997	29.31
1998	29.58
1999	29.85
2000	30.12
2001	30.38
2002	30.65
2003	30.92
2004	31.19
2005	31.45
2006	31.71
2007	31.97
2008	32.22
2009	32.48
2010	32.73
2011	33
2012	33.27
2013	33.53
2014	33.8
2015	34.07