Year	Percent
1960	0.11
1961	0.14
1962	0.14
1963	0.17
1964	0.15
1965	0.16
1966	0.18
1967	0.17
1968	0.29
1969	0.3
1970	0.33
1971	0.34
1972	0.43
1973	0.45
1974	0.57
1975	0.65
1976	0.71
1977	0.84
1978	0.9
1979	0.95
1980	0.87
1981	0.85
1982	1.03
1983	1.1
1984	1.03
1985	1.01
1986	1.17
1987	1.09
1988	1.13
1989	1.05
1990	1.17
1991	1.13
1992	1.16
1993	1.01
1994	1.05
1995	0.86
1996	0.83
1997	0.84
1998	0.89
1999	0.88
2000	0.76
2001	0.8
2002	0.89
2003	0.92
2004	0.87
2005	0.94
2006	0.89
2007	0.95
2008	0.88