Year	Percent
1950	4
1951	4
1952	4
1953	4
1954	5
1955	5
1956	5
1957	5
1958	5
1959	5
1960	5
1961	5
1962	5
1963	5
1964	5
1965	4
1966	5
1967	5
1968	5
1969	5
1970	5
1971	5
1972	5
1973	5
1974	7
1975	7
1976	8
1977	8
1978	15
1979	15
1980	24
1981	24
1982	30
1983	30
1984	28
1985	28
1986	28
1987	31
1988	32
1989	32
1990	38
1991	43
1992	29
1993	35
1994	38
1995	39
1996	35
1997	31
1998	37
1999	34
2000	32
2001	29
2002	31
2003	26
2004	26
2005	27
2006	25