# year    value 
 1901 7.636896 
 1902 6.824128 
 1903 6.816469 
 1904 6.469001 
 1905 6.531796 
 1906 7.407413 
 1907 6.314463 
 1908 6.367952 
 1909 6.278773 
 1910 7.507908 
 1911 6.835064 
 1912 6.532752 
 1913 6.835574 
 1914 7.302135 
 1915 7.081271 
 1916 6.630467 
 1917 6.343109 
 1918 6.830804 
 1919 6.557214 
 1920 7.404738 
 1921 7.646638 
 1922 7.511194 
 1923 6.410583 
 1924 6.612615 
 1925 7.424938 
 1926 6.829817 
 1927 7.036657 
 1928 6.391877 
 1929  6.82659 
 1930 7.495047 
 1931 6.846267 
 1932 6.857844 
 1933 6.727222 
 1934 7.104537 
 1935 6.788403 
 1936 6.844658 
 1937 6.902326 
 1938 7.890867 
 1939 7.067294 
 1940 7.139088 
 1941 7.074974 
 1942 7.057123 
 1943 7.188389 
 1944 7.630764 
 1945 7.206533 
 1946 7.681722 
 1947 7.253808 
 1948 7.288158 
 1949 7.100983 
 1950 7.114698 
 1951 7.387183 
 1952 6.944685 
 1953  7.56403 
 1954 6.233734 
 1955 6.839081 
 1956 6.304038 
 1957  6.94539 
 1958 7.051492 
 1959 7.599837 
 1960 6.217822 
 1961 7.903897 
 1962 7.696229 
 1963  7.27114 
 1964 6.713374 
 1965 6.853472 
 1966 7.405276 
 1967 7.470155 
 1968 8.060789 
 1969 6.509032 
 1970 7.033295 
 1971 6.903077 
 1972 7.202621 
 1973  7.82427 
 1974 7.252878 
 1975 7.715582 
 1976 6.974447 
 1977 8.715489 
 1978 7.407196 
 1979 7.206038 
 1980 7.021142 
 1981  8.12596 
 1982  7.39748 
 1983  7.59526 
 1984 7.302799 
 1985 7.517445 
 1986 8.013374 
 1987 7.353836 
 1988  7.82022 
 1989 7.920485 
 1990 8.572207 
 1991 7.978544 
 1992 7.501132 
 1993 7.623241 
 1994 7.978971 
 1995 8.060055 
 1996 6.828868 
 1997 7.876587 
 1998 8.310423 
 1999   8.0995 
 2000 8.904014 
 2001 8.899119 
 2002 7.978405 
 2003 7.700759 
 2004 8.305643 
 2005 8.358638 
 2006 8.752166 
 2007 8.738306 
 2008  8.86867 
 2009 8.144857 
 2010 8.608642 
 2011 8.182921 
 2012 9.360821 
 2013 8.026183 
 2014  8.42891 
 2015  8.70095 
 2016 9.283405 
 2017 8.874136 
 2018 8.543891