Year	Ratio
1851	660
1855	550
1858	440
1864	833
1865	761.9
1866	637.1
1867	536.8
1868	650.6
1869	702
1870	772.5
1871	936.3
1872	820.9
1874	728.4
1875	836.4
1876	768.8
1877	687.5
1878	698.6
1879	675.1
1880	702.8
1881	735.6
1882	714.5
1883	775.8
1884	789.2
1886	765.1
1887	753.3
1888	665
1889	641
1890	554.1
1891	587.5
1892	645.1
1893	662
1894	574.3
1895	462.1
1896	557.4
1897	497.7
1898	510.4
1900	535.4
1901	523.3
1902	547.1
1903	622
1904	460.7
1905	527
1906	548.1
1907	564.3
1908	505.5
1909	584.1
1910	543.7
1911	591.4
1912	650.4
1913	551.1
1920	604.4
1921	571.7
1922	534.9
1923	563.2
1924	576.3
1925	498.3
1926	613.9
1927	566.7
1928	603.1
1929	619.1
1930	521.9
1931	493.1
1932	480.7
1933	514.8
1934	535.5
1935	415.8
1936	457.1
1937	383.9
1938	401.9
1939	381.5
1940	376
1941	392.6
1942	371.1
1943	381
1944	361.9
1945	342.5
1946	286.3
1947	241
1948	208.1
1949	160.3
1950	148.3
1951	112.4
1952	89.7
1953	84.2
1954	94.3
1955	80.4
1956	57.3
1957	71.3
1958	59.3
1959	51.2
1960	40.7
1961	34.7
1962	32.9
1963	30.8
1964	29.8
1965	23.2
1966	27.1
1967	17.8
1968	21.8
1969	20.5
1970	20.4
1971	18
1972	15.4
1973	14.2
1974	14
1975	11.8
1976	9.7
1977	9.9
1978	10.9
1979	10.9
1980	12.7
1990	10
1995	10
2000	9
2005	7
2010	7
2013	6