Year	Percent
1961	6
1962	6
1963	4
1964	5
1965	5
1966	6
1967	6
1968	5
1969	6
1970	6
1971	5
1972	6
1973	7
1974	9
1975	8
1976	9
1977	9
1978	9
1979	9
1980	11
1981	11
1982	11
1983	11
1984	16
1985	21
1986	21
1987	21
1988	21
1989	21
1990	21