Year	Percent
1990	36.3
1991	36.29
1992	36.36
1993	36.42
1994	36.38
1995	36.21
1996	35.89
1997	35.48
1998	35.05
1999	34.68
2000	34.4
2001	34.16
2002	33.92
2003	33.74
2004	33.62
2005	33.54
2006	33.33
2007	33.12
2008	32.95
2009	32.81
2010	32.67
2011	32.56
2012	32.37
2013	32.19
2014	32.02
2015	31.85
2016	31.77
2017	31.61
2018	31.44
2019	31.28