Year	Percent
1952	4
1953	3
1954	3
1955	3
1956	3
1957	4
1958	4
1959	5
1960	5
1961	5
1962	5
1963	5
1964	5
1965	5
1966	5
1967	5
1968	5
1969	6
1970	7
1971	5
1972	5
1973	6
1974	7
1975	7
1976	7
1977	8
1978	9
1979	8
1980	11
1981	11
1982	18
1983	21
1984	13
1985	11
1986	12
1987	14
1988	12
1989	15
1990	15
1991	13
1992	13
1993	9
1994	7
1995	9
1996	6
1997	5
1998	3