Year	Percent
1983	26.91
1984	27.28
1985	26.95
1986	26.65
1987	26.15
1988	25.97
1989	25.76
1990	25.34
1991	24.5
1992	23.93
1993	23.47
1994	23.4
1995	23.44
1996	23.32
1997	23.37
1998	23.21
1999	22.71
2000	24.42
2001	23.73
2002	22.74
2003	22.46
2004	22.38
2005	22.29
2006	22.36
2007	22.13
2008	21.47
2009	20.04
2010	19.66
2011	19.74
2012	19.73
2013	19.97
2014	19.99
2015	19.87
2016	19.77
2017	19.73