Year	Percent
1963	5
1964	5
1965	6
1966	6
1967	6
1968	5
1969	5
1970	5
1971	6
1972	6
1973	7
1974	9
1975	9
1976	9
1977	9
1978	9
1979	9
1980	9
1981	10
1982	10
1983	10
1984	10
1985	10
1986	10
1987	10
1988	10
1989	10
1990	10
1991	12
1992	12
1993	12
1994	12
1995	12
1996	12
1997	9
1998	9
1999	8
2000	8
2001	7
2002	6
2003	6
2004	6
2005	6
2006	6