Year	Percent
1971	82.02
1972	81.62
1973	82.37
1974	81.97
1975	82.25
1976	80.25
1977	80.94
1978	80.32
1979	80.31
1980	80.96
1981	80.56
1982	79.31
1983	78.75
1984	78.48
1985	78.31
1986	74.77
1987	74.53
1988	73.73
1989	73.48
1990	72.98
1991	73.6
1992	69.8
1993	75.62
1994	84.68
1995	74.19
1996	76.07
1997	72.64
1998	71.62
1999	67.36
2000	63.72
2001	66.4
2002	62.42
2003	62.05
2004	59.73
2005	61.59
2006	61.6
2007	59.92
2008	59.62
2009	62.59
2010	63.87