Year	Percent
1970	4.8
1971	6
1972	6.6
1973	5.6
1974	3.4
1975	2.3
1976	4.5
1977	2.8
1978	2.8
1979	2
1980	2.3
1981	4.5
1982	4.73
1983	4.17
1984	3.54
1985	5.3
1986	4.4
1987	5.3
1988	6
1989	7.3
1990	7.06
1991	5.44
1992	6.36
1993	10.1
1994	11.76
1995	18.8
1996	17.11
1997	14.82
1998	12.65
1999	14.05
2000	15
2001	17.32
2002	19.59
2003	15.36
2004	13.52
2005	11.51
2006	10.08
2007	8.47
2008	7.84
2009	8.65
2010	7.71
2011	7.18
2012	7.22
2013	7.1
2014	7.27
2017	8.35
2018	9.22
2019	9.84
2020	11.46