Year	Percent
1968	5
1969	5
1970	5
1971	5
1972	5
1973	5
1974	6
1975	6
1976	7
1977	7
1978	7
1979	9
1980	9
1981	9
1982	9
1983	9
1984	9
1985	9
1986	8
1987	8
1988	10
1989	10
1990	11
1991	11
1992	12
1993	12
1994	8
1995	9
1996	8
1997	8
1998	7
1999	7
2000	7
2001	7
2002	6
2003	6
2004	6
2005	6
2006	5