Year	Percent
1948	3
1949	3
1950	3
1951	3
1952	4
1953	4
1954	3
1955	4
1956	5
1957	6
1958	4
1959	4
1960	5
1961	6
1962	4
1963	4
1964	7
1965	6
1966	7
1967	8
1968	7
1969	8
1970	7
1971	5
1972	8
1973	13
1974	12
1975	10
1976	15
1977	7
1978	12
1979	17
1980	14
1981	17
1982	14
1983	12
1984	14
1985	10
1986	13
1987	9
1988	8
1989	12
1990	11
1991	11
1993	7
1994	6
1995	7
1996	6
1997	7
1998	4