Year	Percent
1971	64.69
1972	60.91
1973	61.14
1974	64.18
1975	66.57
1976	66.67
1977	64.46
1978	62.11
1979	61.63
1980	63.4
1981	63.03
1982	61.72
1983	63.21
1984	63.67
1985	64.82
1986	64.01
1987	64.6
1988	64.83
1989	64.02
1990	63.28
1991	63.11
1992	59.47
1993	59.8
1994	59.9
1995	58.29
1996	51.12
1997	51.51
1998	50.45
1999	46.8
2000	44.72
2001	45.96
2002	44
2003	43.52
2004	42.93
2005	41.76
2006	41.95
2007	41.23
2008	42.39
2009	45.11
2010	41.69