Year	Percent
1973	12.89
1974	12.72
1975	13.14
1977	7.9
1978	5.97
1979	5.79
1980	5.26
1981	5.79
1982	5.53
1983	5.92
1984	7.52
1985	9.13
1986	8.91
1987	20.55
1988	20.99
1989	20.69
1990	17.68
1991	15.74
1992	17.06
1993	17.68
1994	16.15
1995	15.2
1996	13.26
1997	12.3
1998	11.35
1999	10.86
2000	10.22
2001	8.66
2002	7.76
2003	8.3
2004	6.38
2005	5.81
2006	4.52
2007	3.91
2008	3.52
2009	4.58
2010	3.4075
2011	2.7316
2012	2.8646
2013	2.1105
2014	1.9793
2015	1.9285
2016	2.986