Year	Percent
1948	3
1949	3
1950	3
1951	3
1952	3
1953	3
1954	3
1955	3
1956	3
1957	3
1958	3
1959	4
1960	4
1961	4
1962	4
1963	4
1964	4
1965	5
1966	5
1967	5
1968	5
1969	5
1970	5
1971	5
1972	6
1973	8
1974	9
1975	9
1976	9
1977	10
1978	10
1979	10
1980	10
1981	10
1982	10
1983	10
1984	10
1985	10
1986	10
1987	10
1988	10
1989	10
1990	10
1991	10
1992	10
1993	10
1994	15
1995	17
1996	20
1997	18
1998	17
1999	13
2000	13
2001	10
2002	8
2003	8
2004	8
2005	9
2006	10