Year	Percent
1990	25.81
1991	26.07
1992	26.34
1993	26.6
1994	26.87
1995	27.13
1996	27.4
1997	27.66
1998	27.93
1999	28.19
2000	28.46
2001	28.72
2002	28.99
2003	29.25
2004	29.51
2005	29.78
2006	29.96
2007	30.14
2008	30.33
2009	30.51
2010	30.69
2011	30.88
2012	31.06
2013	31.24
2014	31.42
2015	31.61