Year	Percent
1973	21.42
1974	20.97
1975	19.54
1977	11.64
1978	10.26
1979	8.91
1980	7.76
1981	7.78
1982	7.68
1983	8.03
1984	9.51
1985	9.81
1986	10.4
1987	25.3
1988	23.75
1989	24.46
1990	24.15
1991	23.46
1992	24.04
1993	23.49
1994	22.27
1995	20.62
1996	21.01
1997	19.44
1998	18.82
1999	16.76
2000	15.11
2001	14.47
2002	14.48
2003	13.81
2004	11.21
2005	10.97
2006	8.72
2007	7.92
2008	6.18
2009	6.29
2010	4.3005
2011	4.0098
2012	4.2776
2013	2.9496
2014	2.5659
2015	2.6134
2016	2.9531