Year	Percent
1990	30.07
1991	30.12
1992	30.16
1993	30.2
1994	30.25
1995	30.29
1996	30.33
1997	30.38
1998	30.42
1999	30.46
2000	30.51
2001	31.01
2002	32.03
2003	32.55
2004	33.06
2005	33.61
2006	33.77
2007	33.93
2008	34.09
2009	34.26
2010	34.42
2011	34.58
2012	34.74
2013	34.9
2014	35.06
2015	35.22