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