Year	Percent
1990	33.02
1991	33.03
1992	33.05
1993	33.06
1994	33.07
1995	33.08
1996	33.09
1997	33.11
1998	33.12
1999	33.13
2000	33.13
2001	33.16
2002	33.18
2003	33.21
2004	33.24
2005	33.26
2006	33.35
2007	33.44
2008	33.58
2009	33.66
2010	33.75
2011	33.78
2012	33.81
2013	33.84
2014	33.87
2015	33.9