Year	Ratio
1900	850
1901	800
1902	740
1903	700
1904	790
1905	800
1906	710
1907	720
1908	670
1909	700
1910	690
1911	700
1912	650
1913	680
1914	710
1915	608
1916	622
1917	662
1918	916
1919	737
1920	799
1921	682
1922	664
1923	665
1924	656
1925	647
1926	656
1927	647
1928	692
1929	695
1930	673
1931	661
1932	633
1933	619
1934	593
1935	582
1936	568
1937	489
1938	435
1939	404
1940	376
1941	317
1942	259
1943	245
1944	228
1945	207
1946	157
1947	135
1948	117
1949	90
1950	83
1951	75
1952	68
1953	61
1954	52.4
1955	47
1956	40.9
1957	41
1958	37.6
1959	37.4
1960	37.1
1961	36.9
1962	35.2
1963	35.8
1964	33.3
1965	31.6
1966	29.1
1967	28
1968	24.5
1969	22.2
1970	20.8
1971	19.7
1972	17.6
1973	16.2
1974	14.2
1975	13.2
1976	12.4
1977	11.4
1978	10.5
1979	10.5
1980	12.2
1990	12
1995	11
2000	13
2005	17
2010	27
2013	28