Year	Percent
1958	3
1959	3
1960	3
1961	3
1962	4
1963	4
1964	4
1965	4
1966	5
1967	5
1968	5
1969	5
1970	5
1971	5
1972	5
1973	5
1974	5
1975	5
1976	5
1977	6
1978	6
1979	6
1980	6
1981	7
1982	7
1983	7
1984	7
1985	9
1986	9
1987	9
1988	9
1989	11
1990	12
1991	12
1992	11
1993	9
1994	9
1995	9
1996	8