1844 15.2 1845 12.4 1846 15.6 1847 16.6 1848 18.9 1849 14.9 1850 13.7 1851 15.4 1852 22.3 1853 17.0 1854 15.8 1855 12.9 1856 8.9 1857 11.7 1858 16.6 1859 17.6 1860 17.4 1861 16.3 1862 18.1 1863 19.6 1864 19.0 1865 20.9 1866 18.0 1867 14.2 1868 18.2 1869 20.9 1870 22.2 1871 21.4 1872 23.7 1873 20.2 1874 14.6 1875 11.3 1876 9.6 1877 9.0 1878 7.3 1879 7.0 1880 11.6 1881 13.6 1882 22.9 1883 17.6 1884 14.2 1885 15.4 1886 20.6 1887 16.4 1888 15.4 1889 12.5 1890 10.7 1891 17.1 1892 24.2 1893 17.0 1894 20.7 1895 18.1 1896 18.0 1897 13.6 1898 15.1 1899 13.1 1900 7.5 1901 6.1 1902 6.5 1903 12.0 1904 11.6 1905 15.0 1906 12.5 1907 16.0 1908 17.1 1909 17.2 1910 17.6 1911 15.9 1912 8.9 1913 8.6 1914 11.0 1915 15.6 1916 19.9 1917 18.3 1918 21.6 1919 22.5 1920 17.6 1921 16.6 1922 18.7 1923 10.2 1924 10.2 1925 13.1 1926 19.9 1927 16.6 1928 17.7 1929 19.4 1930 28.6 1931 16.8 1932 19.0 1933 16.3 1934 13.4 1935 15.6 1936 16.2 1937 19.0 1938 23.6 1939 23.2 1940 23.5 1941 24.9 1942 21.8 1943 25.9 1944 17.8 1945 16.4 1946 25.3 1947 25.2 1948 22.6 1949 21.2 1950 24.4 1951 28.7 1952 27.8 1953 22.2 1954 17.2 1955 17.6 1956 24.7 1957 29.3 1958 28.4 1959 30.2 1960 32.9 1961 22.4 1962 21.5 1963 21.2 1964 17.2 1965 14.0 1966 17.3 1967 19.8 1968 22.5 1969 19.9 1970 20.0 1971 20.0 1972 20.6 1973 26.7 1974 30.4 1975 23.7 1976 22.2 1977 20.2 1978 25.5 1979 22.4 1980 18.0 1981 24.4 1982 33.2 1983 29.5 1984 28.9 1985 22.5 1986 21.0 1987 19.0 1988 22.6 1989 30.9 1990 26.4 1991 34.3 1992 27.2 1993 25.4 1994 29.3 1995 21.9 1996 18.5 1997 16.0 1998 21.1 1999 22.3