Year	Percent
1990	36.21
1991	36.19
1992	36.16
1993	36.14
1994	36.11
1995	36.09
1996	36.06
1997	36.04
1998	36.01
1999	35.99
2000	35.96
2001	35.94
2002	35.91
2003	35.89
2004	35.86
2005	35.84
2006	35.81
2007	35.79
2008	35.76
2009	35.74
2010	35.71
2011	35.69
2012	35.66
2013	35.64
2014	35.61
2015	35.59