Year	Percent
1970	2.42
1971	2.67
1972	2.77
1973	2.69
1974	2.86
1975	4.08
1976	4.47
1977	5.01
1978	5.27
1979	6.03
1980	6.42
1981	7.54
1982	8.2
1983	7.92
1984	9.53
1985	10.26
1986	10.23
1987	10.74
1988	10.18
1989	9.62
1990	9.36
1991	9.13
1992	10.21
1993	11.32
1994	12.59
1995	11.84
1996	12.37
1997	12.57
1998	12.07
1999	11.98
2000	10.22
2001	8.61
2002	8.7
2003	8.31
2004	8.91
2005	8.49
2006	8.45
2007	7.66
2008	7.06
2009	8.74
2010	8.87
2011	8.81
2012	9.4
2013	9.92
2014	10.29
2015	10.35
2016	10.05
2017	9.41
2018	9.02
2019	8.41
2020	8.01