Year	Percent
1974	6
1975	6
1976	6
1977	6
1978	6
1979	7
1980	7
1981	7
1982	7
1983	7
1984	7
1985	7
1986	5
1987	7
1988	7
1989	7
1990	9
1991	10
1992	11
1993	10
1994	10
1995	10
1996	10
1997	12
1998	12
1999	12
2000	14
2001	14
2002	16
2003	15
2004	15
2005	15
2006	11