Year	Percent
1973	50.07
1974	51.74
1975	52.63
1976	54.53
1977	58.11
1978	61.29
1979	61.03
1982	70
1983	78.24
1984	79.16
1985	79.91
1986	71.49
1987	82.39
1988	84.99
1989	82.58
1990	73.31
1992	73.06
1993	73.41
1994	71.43
1995	67.11
1996	65.92
1997	68.05
1998	65.71
1999	75.42
2004	64.25
2013	72.88
2015	70.78