Year	Percent
1975	9.21
1976	5.4
1977	4.4
1978	1.4
1979	2.04
1980	2.29
1981	1.55
1982	1.83
1983	2.11
1984	1.85
1985	3.49
1986	2.99
1987	1.71
1988	1.35
1989	1.08
1990	1.32
1991	1.94
1992	2
1993	1.97
1994	2.02
1995	3.39
1996	3.12
1997	2.31
1998	4.96
1999	6.7
2000	5.56
2001	5.97
2002	8.35
2003	9.17
2004	7.69
2005	6.54
2006	5.63
2007	4.53
2008	4.05
2009	6.07
2010	5.01
2011	3.98
2012	3.77
2013	3.8
2014	3.57
2015	3.43
2016	3.69
2017	3.39