Year	Percent
1971	64.93
1972	63.28
1973	61.13
1974	59.62
1975	62.53
1976	58.24
1977	55.87
1978	58.92
1979	56.83
1980	54.93
1981	56.12
1982	56.82
1983	57.92
1984	56.02
1985	57
1986	58.62
1987	59.27
1988	62.39
1989	61.05
1990	60.06
1991	60.27
1992	58.94
1993	60.91
1994	60.9
1995	59.68
1996	59.79
1997	58.57
1998	57.02
1999	55.27
2000	57.6
2001	56.19
2002	54.23
2003	55.17
2004	50.71
2005	52.35
2006	54.72
2007	49.55
2008	47.21
2009	50.3
2010	50.05