Year	Percent
1970	7.1
1971	7.6
1972	6.79
1973	6.99
1974	5.8
1975	6.41
1976	6.67
1977	8.73
1978	8.06
1979	8.78
1982	8.41
1983	9.71
1984	10.08
1985	12.34
1986	10.53
1987	11.84
1988	16.33
1989	16.31
1990	11.6
1991	16.12
1992	14.67
1993	13.26
1994	14
1995	14.01
1996	14.32
1997	13.37
1998	14.02
1999	11.75
2000	13.53
2001	14.71
2002	14.11
2003	13.62
2004	12.44
2005	10.33
2006	9.11
2007	6.78
2008	4.87
2009	6.56
2010	3.71
2011	2.31
2012	2.39
2013	2.3
2014	2.72
2015	3
2016	3.31
2017	3.9
2018	3.89
2019	4.74
2020	18.55