Year	Ratio
1952	183.7
1953	164.8
1954	148.2
1955	153.3
1956	139.2
1957	127.3
1958	118.4
1959	108.6
1960	106.3
1961	97.7
1962	87.1
1963	82.8
1964	69.4
1965	69.3
1966	65.1
1967	58.2
1968	51.6
1969	53.1
1970	51.8
1971	48.4
1972	46.4
1973	40.9
1974	39.9
1975	36.7
1976	36.7
1977	31.9
1978	27.2
1979	27.2
1980	20.5
1990	13
1995	8
2000	7
2005	7
2010	7
2013	7