Year	Percent
1971	57.45
1972	55.64
1973	51.58
1974	51.85
1975	56.46
1976	56.8
1977	56.6
1978	58.27
1979	58.3
1980	56.82
1981	57.61
1982	57.34
1983	57.91
1984	58.78
1985	57.33
1986	58.13
1987	61.45
1988	56.92
1989	58.15
1990	54.54
1991	56.67
1992	57.56
1993	63.44
1994	59.2
1995	61.04
1996	60.38
1997	57.73
1998	58.21
1999	58.78
2000	58.18
2001	57.6
2002	57.45
2003	56
2004	54.61
2005	55.24
2006	51.59
2007	48.98
2008	48.26
2009	47.73
2010	47.69