Year	Percent
1990	26.36
1991	26.52
1992	26.68
1993	26.83
1994	26.99
1995	27.14
1996	27.3
1997	27.45
1998	27.61
1999	27.77
2000	27.92
2001	28.13
2002	28.34
2003	28.53
2004	28.76
2005	28.97
2006	29.17
2007	29.38
2008	29.58
2009	29.79
2010	30
2011	30.2
2012	30.41
2013	30.61
2014	30.82
2015	31.03