Year	Percent
1976	12
1977	12
1978	12
1979	12
1980	12
1981	12
1982	15
1983	15
1984	15
1985	15
1986	11
1987	11
1988	11
1989	11
1990	11
1991	13
1992	13
1993	11
1994	11
1995	11
1996	11
1997	9
1998	9
1999	9
2000	8
2001	7
2002	6
2003	6
2004	6
2005	6
2006	6