Year	Percent
1968	0.97
1969	0.89
1970	0.88
1971	0.97
1972	1.03
1973	0.93
1974	1.1
1975	1.57
1976	1.63
1977	1.62
1978	1.87
1979	1.7
1980	1.66
1981	1.8
1982	1.9
1983	2.22
1984	2.19
1985	2.12
1986	2.21
1987	2.25
1988	1.98
1989	1.78
1990	1.64
1991	1.64
1992	1.7
1993	2
1994	2.34
1995	2.59
1996	2.72
1997	2.83
1998	3.44
1999	3.96
2000	4.06
2001	4.39
2002	4.89
2003	4.7
2004	4.38
2005	4.19
2006	3.94
2007	3.73
2008	3.88
2009	4.96
2010	4.92
2011	4.42
2012	4.26
2013	4.09
2014	3.59
2015	3.43
2016	3.14
2017	2.82
2018	2.48
2019	2.39
2020	2.82