Year	Percent
1960	0.31
1961	0.45
1962	0.49
1963	0.26
1964	0.29
1965	0.36
1966	0.45
1967	0.49
1968	0.49
1969	0.5
1970	0.62
1971	0.58
1972	0.67
1973	0.53
1974	0.61
1975	0.74
1976	0.8
1977	0.81
1978	0.78
1979	0.94
1980	0.97
1981	1.07
1982	1.07
1983	0.91
1984	1.02
1985	0.91
1986	1.01
1987	0.98
1988	0.98
1989	0.94
1990	0.92
1991	0.88
1992	0.86
1993	0.82
1994	0.76
1995	0.81
1996	0.81
1997	0.81
1998	0.8
1999	0.79
2000	0.84
2001	0.82
2002	0.81
2003	0.8
2004	0.73
2005	0.82
2006	0.81
2007	0.81
2008	0.8