Year	Percent
1971	75.14
1972	74.91
1973	75.69
1974	76.13
1975	73.32
1976	76.1
1977	73.5
1978	73.96
1979	71.79
1980	71.83
1981	72.21
1982	70.78
1983	76.29
1984	78.31
1985	76.47
1986	70.84
1987	70.13
1988	71.41
1989	71.52
1990	70.32
1991	72
1992	74.83
1993	79.06
1994	71.73
1995	70.78
1996	63.81
1997	70.42
1998	69.7
1999	67.14
2000	71.12
2001	74.41
2002	71.5
2003	69.58
2004	70.13
2005	72.29
2006	73.31
2007	73.14
2008	69.44
2009	69.26
2010	69.14