1950	3.3
1951	3.4
1952	5.3
1953	6.4
1954	5.8
1955	8.5
1956	10.9
1957	11.0
1958	7.7
1959	6.9
1960	5.9
1961	4.4
1962	4.1
1963	3.3
1964	6.3
1965	10.2
1966	8.4
1967	10.8
1968	18.4
1969	17.7
1970	12.6
1971	9.2
1972	4.3
1973	3.6
1974	5.2
1975	8.5
1976	11.7
1977	7.4
1978	8.0
1979	6.5
1980	2.7
1981	2.6
1982	4.0
1983	4.7
1984	2.9
1985	3.9
1986	3.2
1987	16.2
1988	21.9
1989	6.7
1990	6.8
1991	7.5
1992	13.5
1993	19.7
1994	19.6
1995	17.5
1996	9.3
1997	8.6
1998	9.5
1999	17.0