Year	Percent
1968	0
1969	0
1970	0
1971	0
1972	0
1973	0
1974	0
1975	0
1976	0
1977	0
1978	0
1979	0
1980	0
1981	1
1982	1
1983	0.9
1984	0.9
1985	0.9
1986	0.9
1987	0.8
1988	0.8
1989	0
1990	0
1991	0
1992	0.6
1993	0.6
1994	0.6
1995	0.6
1996	0.6
1997	0.6
1998	0.6
1999	0.5
2000	1.1
2001	1.1
2002	1.1
2003	1.1
2004	1.1
2005	1.1
2006	1
2007	1
2008	1.4
2009	1.4
2010	1.3
2011	0.939
2012	1.3
2013	1.2
2014	1.5
2015	1
2016	1.3
2017	1.2