Year	Percent
1971	73.84
1972	73.44
1973	73.49
1974	73.27
1975	72.32
1976	73.2
1977	70.84
1978	70.71
1979	70.6
1980	70.77
1981	70.07
1982	68.83
1983	67.84
1984	67.35
1985	66.91
1986	67.77
1987	68.04
1988	67.65
1989	68.5
1990	69.31
1991	70.63
1992	70.67
1993	70.17
1994	70.54
1995	71.26
1996	71.47
1997	71.21
1998	71.39
1999	72.29
2000	71.73
2001	71.85
2002	71.34
2003	71.32
2004	70.83
2005	71.2
2006	77.29
2007	72.24
2008	71.77
2009	70.61
2010	69.97