Year	Percent
1970	2.4
1971	1.82
1972	1.53
1973	1.71
1974	2.3
1975	2.57
1977	3.13
1978	3.64
1979	4.55
1980	5.18
1981	4.97
1982	5.21
1983	6.47
1984	5.89
1989	7.06
1990	8.43
1991	9.38
1992	8.92
1993	10.92
1994	10.93
1995	11.04
1996	9
1997	8.37
1998	8.03
1999	7.95
2000	8.98
2001	9.26
2002	10.01
2003	11.01
2004	10.32
2005	11.2
2006	10.49
2007	8.8
2008	8.52
2009	9.09
2010	8.76
2011	11.85
2012	12.6
2013	13.15
2014	13.1
2015	13.05
2016	12.41
2017	11.74
2018	9.82
2019	7.84