Year	Percent
1969	13.17
1970	12.76
1971	13.03
1973	15.4
1974	15.24
1975	14.99
1977	8.98
1978	7.27
1979	6.75
1980	6.03
1981	6.31
1982	6.22
1983	6.61
1984	8.17
1985	9.31
1986	9.37
1987	22.11
1988	21.88
1989	21.95
1990	19.87
1991	18.52
1992	19.66
1993	19.81
1994	18.44
1995	17.22
1996	16.25
1997	15.01
1998	14.21
1999	13.12
2000	12.1
2001	10.88
2002	10.39
2003	10.48
2004	8.33
2005	7.95
2006	6.27
2007	5.54
2008	4.63
2009	5.28
2010	4.03
2011	3.43
2012	3.72
2013	2.68
2014	2.48
2015	2.43
2016	3.21