Year	Percent
1971	69.05
1972	67.98
1973	66.84
1974	66.65
1975	66.01
1976	65.73
1977	64.32
1978	63.32
1979	62.09
1980	60.63
1981	61.78
1982	61.99
1983	60.52
1984	59.64
1985	60.27
1986	60.13
1987	57.2
1988	56
1989	54.52
1990	55.68
1991	55.94
1992	54.77
1993	53.81
1994	52.61
1995	53.03
1996	52
1997	55.11
1998	53.41
1999	44.08
2000	48.22
2001	43.59
2002	43
2003	42.15
2004	43.46
2005	44.47
2006	46.28
2007	44.83
2008	46.94
2009	47.79
2010	48.31