Year	Percent
1971	2.09
1972	2.15
1973	2
1974	1.67
1975	1.7
1976	1.9
1977	1.9
1978	4.18
1979	4.12
1980	4.01
1981	3.82
1982	3.82
1983	4.3
1984	4.16
1985	3.97
1986	3.97
1987	3.05
1988	2.16
1989	2.03
1990	1.97
1991	5.85
1992	5.18
1993	4.28
1994	4.26
1995	5.03
1996	4.79
1997	5.81
1998	5.7
1999	5.35
2000	7.16
2001	6.88
2002	7.83
2003	7.49
2004	7.4
2005	7.05
2006	0.58
2007	0.4
2008	0.42
2009	0.54
2010	0.65
2011	0.8
2013	2.95
2014	1.83
2015	3.57
2018	4.08