Year	Percent
1990	29.12
1991	29.23
1992	29.34
1993	29.44
1994	29.55
1995	29.66
1996	29.77
1997	29.88
1998	29.99
1999	30.1
2000	30.21
2001	30.33
2002	30.44
2003	30.56
2004	30.68
2005	30.8
2006	30.89
2007	30.98
2008	31.07
2009	31.16
2010	31.25
2011	31.35
2012	31.45
2013	31.54
2014	31.64
2015	31.73