Year	Percent
1971	64.47
1972	64.43
1973	63.46
1974	64.1
1975	59.99
1976	50.97
1977	47.35
1978	42.45
1979	49.2
1980	50.57
1981	46.38
1982	51.29
1983	51.56
1984	55.24
1985	54.86
1986	55.06
1987	56.34
1988	53.48
1989	59.44
1990	64.67
1991	62.56
1992	62.1
1993	60.23
1994	60.28
1995	59.42
1996	59.13
1997	58.05
1998	57.4
1999	59.73
2000	61.88
2001	57.77
2002	58.31
2003	58.35
2004	58.95
2005	56.04
2006	57.24
2007	55.47
2008	55.72
2009	54.88
2010	54.08