Year	Percent
1960	23.4
1961	20.5
1962	19.62
1963	18.58
1964	15.58
1965	14.34
1966	12.88
1967	11.81
1968	10.41
1969	9.168
1970	8.233
1971	8.022
1972	7.487
1973	7.609
1974	7.708
1975	8.093
1976	8.017
1977	7.834
1978	32.35
1979	32.42
1980	32.47
1981	32.07
1982	32.23
1983	30.36
1984	31.67
1985	29.68
1986	30.36
1987	30.33
1988	29.83
1989	29.13
1990	28.25
1991	28.62
1992	28.8
1993	31.32
1994	30.72
1995	32.02
1996	31.87
1997	30.44
1998	30.93
1999	29.58
2000	28.49
2001	29.25
2002	29.13
2003	29.82
2004	29.72
2005	30.1
2006	29.51
2007	28.12
2008	29.1
2009	29.6
2010	30.69