# year value 1901 6.199363 1902 5.883105 1903 5.856492 1904 5.836889 1905 5.89526 1906 6.141666 1907 5.55419 1908 5.793488 1909 5.852639 1910 6.044447 1911 5.840811 1912 5.559336 1913 5.999804 1914 6.23115 1915 6.179022 1916 5.822335 1917 5.675889 1918 5.940259 1919 5.786849 1920 5.921973 1921 6.3764 1922 6.027794 1923 6.118943 1924 5.930259 1925 6.410138 1926 6.229365 1927 6.096956 1928 5.99858 1929 5.565926 1930 6.246301 1931 6.221786 1932 6.326353 1933 5.808082 1934 6.345905 1935 6.083812 1936 6.120928 1937 6.106166 1938 6.589315 1939 6.555632 1940 6.220935 1941 6.229496 1942 6.10261 1943 6.347296 1944 6.430423 1945 5.983192 1946 6.399776 1947 6.220875 1948 6.51057 1949 6.254972 1950 5.84783 1951 6.131971 1952 6.197814 1953 6.568766 1954 6.002344 1955 6.345382 1956 5.668652 1957 6.139662 1958 6.446289 1959 6.236054 1960 6.168694 1961 6.603249 1962 6.466275 1963 6.512894 1964 5.956351 1965 6.018569 1966 6.261423 1967 6.215574 1968 6.160894 1969 5.636863 1970 6.156303 1971 6.356402 1972 5.719525 1973 6.546055 1974 6.081578 1975 6.569221 1976 5.856501 1977 6.491342 1978 6.236472 1979 6.37472 1980 6.278632 1981 6.932093 1982 6.32656 1983 6.80041 1984 6.143197 1985 6.049151 1986 6.524944 1987 6.566045 1988 6.819425 1989 6.830188 1990 7.168651 1991 6.783163 1992 6.518674 1993 6.316416 1994 6.888136 1995 7.129692 1996 6.275736 1997 6.859851 1998 7.361715 1999 7.431127 2000 7.024742 2001 7.292842 2002 7.264273 2003 7.038678 2004 7.222356 2005 7.212891 2006 7.445947 2007 7.574523 2008 7.257182 2009 6.992707 2010 7.286646 2011 7.097534 2012 7.258273 2013 7.269231 2014 7.189088 2015 7.775247 2016 7.750423 2017 7.698007 2018 7.396747