Year	Percent
1990	35.74
1991	35.64
1992	35.54
1993	35.44
1994	35.34
1995	35.25
1996	35.15
1997	35.05
1998	34.95
1999	34.85
2000	34.75
2001	34.66
2002	34.56
2003	34.46
2004	34.36
2005	34.26
2006	34.16
2007	34.07
2008	33.97
2009	33.87
2010	33.77
2011	33.67
2012	33.57
2013	33.48
2014	33.38
2015	33.28