Year	Percent
1964	3
1965	3
1966	3
1967	3
1968	3
1969	3
1970	3
1971	3
1972	3
1973	5
1974	7
1975	7
1976	6
1977	6
1978	6
1979	9
1980	10
1981	13
1982	12
1983	12
1984	12
1985	20
1986	22
1987	22
1988	22
1989	22
1990	22
1991	18
1992	16
1993	20
1994	16
1995	19
1996	25
1997	30
1998	30
1999	25
2000	20
2001	20
2002	20
2003	20
2004	20
2005	12
2006	12