Year	Percent
1976	20.18
1977	20.3
1978	20.6
1979	20.7
1980	20.6
1981	19.74
1982	17.29
1983	17.41
1984	16.76
1985	16.02
1986	12.7
1987	12.84
1988	12.84
1989	12.84
1990	12.84
1991	29.44
1992	31.42
1993	28.21
1994	29.57
1995	28.75
1996	28.26
1997	29.68
1999	18.91
2000	18.6
2001	15.68
2002	17.75
2003	20.52
2004	20.52
2005	19.39
2006	17.46
2007	19.67
2008	20.08
2009	20.69
2011	20.93
2012	20.59
2013	19.83
2014	20.62
2015	22.5
2016	20.98
2017	21.63