Year	Percent
1964	4
1965	4
1966	4
1967	4
1968	4
1969	4
1970	4
1971	4
1972	4
1973	6
1974	6
1975	8
1976	8
1977	8
1978	8
1979	8
1980	11
1981	11
1982	13
1983	11
1984	11
1985	11
1986	9
1987	9
1988	10
1989	11
1990	11
1991	11
1992	13
1993	6
1994	6
1995	6
1996	6
1997	6
1998	6
1999	6
2000	6
2001	6
2002	6
2003	5
2004	4
2005	4
2006	4