Year	Percent
1976	13.12
1977	17.8
1978	15.86
1979	12.47
1980	11.31
1981	9.52
1982	10.41
1983	11.24
1984	22.07
1985	24.2
1986	22.97
1987	23.27
1988	23.34
1989	18.73
1990	10.44
1991	8.55
1992	25.79
1993	27.66
1994	27.91
1995	22.71
1996	17.65
1997	17.99
1998	16.52
1999	13.41
2000	11.47
2001	11.81
2002	12.14
2003	12.55
2004	10.43
2005	10.77
2006	9.84
2007	8.45
2008	9.45
2009	9.89
2010	10.47
2011	12.63
2012	12.27
2013	11.43
2014	12.78
2015	10.32
2016	10.01