Year	Percent
1970	14.8
1973	26.3
1975	36.7
1978	53.4
1979	53.4
1981	59
1984	64.6
1987	65.5
1989	66.2
1993	73.9
1996	75.2
1997	72.2
2000	79.2
2001	77.8
2005	71.5
2006	71.5
2009	79.6
2012	79.3
2016	78.4