Year	Percent
1970	6
1971	6
1972	5
1973	6
1974	10
1975	9
1976	9
1977	10
1978	9
1979	10
1980	11
1981	14
1982	16
1983	12
1984	12
1985	16
1986	17
1987	15
1988	13
1989	17
1990	15
1991	11
1992	7
1993	6
1994	6
1995	6