# year    value 
 1901 7.816354 
 1902 8.158642 
 1903 8.037361 
 1904 7.580984 
 1905 7.755324 
 1906 8.023082 
 1907 7.754038 
 1908 7.831136 
 1909 7.739978 
 1910 7.977878 
 1911 7.531645 
 1912 8.029801 
 1913 7.778919 
 1914 8.571909 
 1915  8.16728 
 1916 8.095892 
 1917 7.354601 
 1918 7.385801 
 1919 7.891678 
 1920 7.878349 
 1921   8.0974 
 1922 7.757068 
 1923 7.978878 
 1924 8.084961 
 1925 7.904482 
 1926  8.62567 
 1927 7.912397 
 1928 8.018193 
 1929 7.635036 
 1930  7.79013 
 1931 8.102257 
 1932 8.522028 
 1933 7.878381 
 1934 8.008833 
 1935 8.424309 
 1936 7.831457 
 1937 8.392113 
 1938 8.303738 
 1939 8.282458 
 1940 8.327812 
 1941 8.305541 
 1942 8.080734 
 1943 8.165452 
 1944 8.820424 
 1945  7.94674 
 1946 8.082296 
 1947 7.888506 
 1948 8.333342 
 1949 8.129086 
 1950 7.620652 
 1951 7.616234 
 1952 8.500229 
 1953 8.358471 
 1954 7.920656 
 1955 8.394291 
 1956 7.601378 
 1957 7.912855 
 1958 8.719239 
 1959 8.246702 
 1960 8.373444 
 1961 8.522755 
 1962 8.322516 
 1963  8.36328 
 1964 8.087575 
 1965 7.895635 
 1966 8.032486 
 1967 7.706059 
 1968 8.021658 
 1969 7.494415 
 1970 8.403625 
 1971 7.885116 
 1972 7.551875 
 1973 8.500979 
 1974 7.739703 
 1975  8.18449 
 1976 7.984254 
 1977 7.941754 
 1978 8.197872 
 1979 7.853705 
 1980 8.549762 
 1981 8.818406 
 1982 8.319162 
 1983 8.879519 
 1984 8.305871 
 1985 7.791785 
 1986 8.464876 
 1987 8.503933 
 1988 8.734526 
 1989 8.563802 
 1990 8.628619 
 1991 8.694759 
 1992  8.65613 
 1993 8.637496 
 1994 8.144565 
 1995 9.100337 
 1996   8.4493 
 1997 8.622538 
 1998 9.084003 
 1999 9.238876 
 2000 9.047227 
 2001 8.581928 
 2002  9.30528 
 2003 8.826143 
 2004 9.263003 
 2005 8.891158 
 2006  9.09683 
 2007 9.557372 
 2008 8.710718 
 2009 8.956661 
 2010 8.901833 
 2011 8.667655 
 2012 8.861648 
 2013 8.898762 
 2014 8.853686 
 2015 9.327842 
 2016 10.03527 
 2017 9.467077 
 2018 9.233799