Year	Percent
1960	26.45
1961	25.48
1962	23.28
1963	22.49
1964	22
1965	21.06
1966	20.87
1967	21.01
1968	20.24
1969	19.21
1970	17.15
1971	16.43
1972	14.9
1973	14.09
1974	12.68
1975	13.23
1976	13.69
1977	13.91
1978	14.31
1979	12.6
1980	13.01
1981	14.27
1982	13.35
1983	13.83
1984	13.69
1985	13.88
1986	13.38
1987	13.19
1988	12.51
1989	18.12
1990	17.12
1991	17.48
1992	17.32
1993	17.78
1994	17.26
1995	16.84
1996	16.81
1997	15.96
1998	14.87
1999	15.02
2000	14.43
2001	14.64
2002	14.96
2003	15.57
2004	15.65
2005	15.66
2006	16.24
2007	15.81
2008	16
2009	16.92
2010	15.12