Year	Percent
1960	14.35
1961	14.88
1962	16.7
1963	19.28
1964	16.76
1965	15.38
1966	16.19
1967	15.62
1968	16.27
1969	16.26
1970	16.9
1971	16.79
1972	18.57
1973	17.67
1974	16.13
1975	18.01
1976	18.11
1977	19.63
1978	18.71
1979	20.28
1980	19.66
1981	20.77
1982	21.67
1983	22.87
1984	20.96
1985	21.43
1986	23.12
1987	22.64
1988	20.9
1989	18.72
1990	17.83
1991	19.59
1992	18.59
1993	18.11
1994	17.91
1995	19.92
1996	21.34
1997	20.62
1998	21.55
1999	9.658
2000	14.53
2001	14.96
2002	14.41
2003	14.14
2004	13.48
2005	12.99
2006	12.92
2007	12.86
2008	12.99
2009	14.09
2010	12.48