Year	Percent
1990	37.55
1991	37.45
1992	37.35
1993	37.25
1994	37.15
1995	37.04
1996	36.94
1997	36.84
1998	36.74
1999	36.64
2000	36.54
2001	36.43
2002	36.33
2003	36.23
2004	36.12
2005	36.03
2006	35.91
2007	35.78
2008	35.66
2009	35.49
2010	35.36
2011	35.24
2012	35.12
2013	34.99
2014	34.86
2015	34.74