Year	Percent
1992	31.27
1993	31.39
1994	31.51
1995	31.63
1996	31.75
1997	31.87
1998	31.99
1999	32.11
2000	32.23
2001	32.55
2002	32.87
2003	33.19
2004	33.52
2005	33.84
2006	33.99
2007	34.15
2008	34.31
2009	34.47
2010	34.62
2011	34.66
2012	34.69
2013	34.72
2014	34.76
2015	34.8