Year	Percent
1969	1.3
1970	1.1
1971	1.5
1972	1.5
1973	2.49
1974	3.04
1975	4.8
1976	2.9
1977	5.2
1978	6.97
1979	8.61
1980	11.4
1981	14.17
1982	16
1983	17.49
1984	20.25
1985	21.64
1986	21.26
1987	20.61
1988	19.85
1989	17.33
1990	16.27
1991	15.93
1992	17.7
1993	22.16
1994	24.21
1995	22.67
1996	22.14
1997	20.7
1998	18.67
1999	15.48
2000	13.79
2001	10.35
2002	11.15
2003	11.28
2004	11.09
2005	9.15
2006	8.45
2007	8.23
2008	11.25
2009	17.86
2010	19.86
2011	21.39
2012	24.79
2013	26.09
2014	24.44
2015	22.06
2016	19.63
2017	17.22
2018	15.25
2019	14.1
2020	15.53