Year	Percent
1960	7.248
1961	9.49
1962	12.54
1963	13.76
1964	13.86
1965	16.51
1966	18.4
1967	18.85
1968	20.78
1969	19.6
1970	21.32
1971	21.46
1972	21.74
1973	22.36
1974	19.14
1975	22.77
1976	23.16
1977	24.95
1978	25.23
1979	24.46
1980	23.11
1981	21.25
1982	20.59
1983	19.68
1984	22.03
1985	24.71
1986	24.45
1987	24.7
1988	22.82
1989	21.8
1990	23.98
1991	25.18
1992	25.1
1993	24.2
1994	23.84
1995	24.36
1996	23.57
1997	22.36
1998	22.28
1999	21.25
2000	18.51
2001	19.93
2002	19.66
2003	19.81
2004	19.05
2005	19.84
2006	19.37
2007	19.3
2008	19.23
2009	21.6
2010	21.58