Year	Percent
1948	7
1949	6
1950	8
1951	6
1952	6
1953	6
1954	6
1955	6
1956	8
1957	8
1958	7
1959	7
1960	7
1961	7
1962	7
1963	7
1964	7
1965	7
1966	7
1967	7
1968	7
1969	7
1970	7
1971	9
1972	8
1973	9
1974	9
1975	9
1976	9
1977	8
1978	7
1979	9
1980	9
1981	9
1982	9
1983	10
1984	10
1985	9
1986	7
1987	7
1988	8
1989	9
1990	9
1991	9
1992	10
1993	6
1994	5
1995	5
1996	4
1997	4
1998	4