Year	Percent
1983	10.25
1984	11.23
1985	10.61
1986	10.08
1987	9.98
1988	9.49
1989	8.25
1990	7.37
1991	7.32
1992	8.94
1993	8.51
1994	7.95
1995	7.68
1996	7.22
1997	6.85
1998	6.6
1999	5.77
2000	5.81
2001	6.09
2002	5.89
2003	5.91
2004	3.63
2005	2.81
2006	2.71
2007	2.62
2008	2.48
2009	2.2
2010	2.28
2011	2.23
2012	1.99
2013	2.01
2014	1.95
2015	1.86
2016	1.77
2017	1.65