Year	Percent
1983	0.98
1984	0.88
1985	0.65
1986	0.69
1987	0.64
1988	0.6
1989	0.45
1990	0.52
1991	0.39
1992	0.41
1993	0.41
1994	0.44
1995	0.42
1996	0.33
1997	0.38
1998	0.38
1999	0.31
2000	0.32
2001	0.44
2002	0.44
2003	0.41
2004	0.49
2005	0.51
2006	0.44
2007	0.44
2008	0.41
2009	0.31
2010	0.3
2011	0.34
2012	0.33
2013	0.28
2014	0.25
2015	0.24
2016	0.23
2017	0.22