Year	Percent
1974	7.4
1975	10.35
1976	10.37
1977	12.8
1978	12.36
1979	13.47
1982	13.29
1983	14.48
1984	14.17
1985	18.47
1986	14.49
1987	16.75
1988	21.37
1989	21.6
1991	22.57
1992	22.32
1993	20.17
1994	20.38
1995	20.14
1996	20
1997	18.14
1998	20.84
1999	16.93
2000	18.03
2001	19.31
2002	19.17
2003	18.82
2004	17.42
2005	13.95
2006	12.37
2007	9.27
2009	8.85
2010	5.0694
2011	2.683
2012	3.0321
2013	3.0585
2014	3.4942
2015	3.9
2016	3.9209
2017	5.0762