Year	Percent
1976	31.72
1977	32
1978	32
1979	32.4
1980	32.9
1981	33.92
1982	36.3
1983	35.17
1984	35.97
1985	36.55
1986	39.86
1987	39.79
1988	39.78
1989	39.78
1990	39.78
1991	68.79
1992	66.42
1993	69.91
1994	68.8
1995	68.99
1996	66.44
1997	64.62
1999	41.14
2000	42.4
2001	40.11
2002	39.86
2003	44.4
2004	44.4
2005	42
2006	43.04
2007	44.23
2008	48.67
2009	49.18
2011	49.26
2012	51.59
2013	50.92
2014	48.51
2015	49.56
2016	49.7
2017	50.17