Year	Percent
1960	1.35
1961	1.36
1962	1.27
1963	0.98
1964	0.9
1965	0.76
1966	0.69
1967	0.71
1968	0.67
1969	0.67
1970	0.52
1971	0.51
1972	0.49
1973	0.43
1974	0.44
1975	0.44
1976	0.41
1977	0.38
1978	0.39
1979	0.42
1980	0.44
1981	0.51
1982	0.56
1983	0.56
1984	0.62
1985	0.61
1986	0.56
1987	0.6
1988	0.58
1989	0.61
1990	0.6
1991	0.62
1992	0.63
1993	0.63
1994	0.62
1995	0.55
1996	0.48
1997	0.44
1998	0.38
1999	0.38
2000	0.3
2001	0.31
2002	0.37
2003	0.4
2004	0.41
2005	0.47
2006	0.47
2007	0.38
2008	0.39