Year	Percent
1983	30.59
1984	30.31
1985	29.8
1986	29.58
1987	28.63
1988	28.55
1989	28.69
1990	28.67
1991	28.93
1992	27.99
1993	27.06
1994	27.72
1995	27.69
1996	27.23
1997	28.47
1998	28.68
1999	28.3
2000	28.46
2001	28.93
2002	27.62
2003	27.74
2004	27.58
2005	27.6
2006	27.61
2007	25.65
2008	23.2
2009	19.78
2010	18.01
2011	17.41
2012	16.95
2013	17.21
2014	17.27
2015	18.04
2016	18.5
2017	18.76