Year	Percent
1966	6
1967	7
1968	6
1969	6
1970	6
1971	5
1972	5
1973	6
1974	6
1975	6
1976	6
1977	6
1978	6
1979	6
1980	6
1981	6
1982	6
1983	8
1984	8
1985	8
1986	6
1987	8
1988	10
1989	10
1990	10
1991	12
1992	13
1993	13
1994	13
1995	13
1996	13
1997	13
1998	13
1999	13
2000	13
2001	13
2002	7
2003	7
2004	7
2005	8
2006	10