# year    value 
 1901 8.246445 
 1902 7.582764 
 1903  7.83886 
 1904 8.230134 
 1905 7.708066 
 1906 7.764442 
 1907 7.806458 
 1908 7.754506 
 1909 8.000031 
 1910 8.221393 
 1911 7.946998 
 1912 8.186697 
 1913 8.583292 
 1914  8.62902 
 1915 8.404448 
 1916 7.650611 
 1917  8.20363 
 1918 8.116255 
 1919 8.381448 
 1920 8.131677 
 1921 7.963158 
 1922 7.953092 
 1923 7.760384 
 1924 7.936024 
 1925 7.811905 
 1926 8.298114 
 1927 8.116232 
 1928 8.206976 
 1929  8.07142 
 1930 8.245689 
 1931 7.727933 
 1932 8.170481 
 1933 8.058716 
 1934 8.388905 
 1935 8.283894 
 1936 8.271131 
 1937 8.034105 
 1938  7.94838 
 1939 8.592961 
 1940 8.692257 
 1941 8.784838 
 1942 7.833263 
 1943 7.732555 
 1944 8.335869 
 1945 8.512184 
 1946 8.130165 
 1947 8.373406 
 1948 8.046741 
 1949 8.347702 
 1950 8.486578 
 1951 8.654859 
 1952  8.12939 
 1953  8.13247 
 1954 8.110852 
 1955 7.587387 
 1956 8.086326 
 1957 8.092854 
 1958 8.598742 
 1959 8.558102 
 1960 7.971181 
 1961 8.325955 
 1962 8.525268 
 1963 8.436638 
 1964 7.986964 
 1965 8.523039 
 1966 8.147429 
 1967 7.916221 
 1968 8.614458 
 1969 8.513887 
 1970 8.322034 
 1971 8.168054 
 1972 8.229033 
 1973 8.319805 
 1974 8.377912 
 1975 8.462251 
 1976 8.091305 
 1977 8.653758 
 1978 8.354503 
 1979 8.939377 
 1980 8.547758 
 1981 8.454328 
 1982 8.178693 
 1983 8.050206 
 1984 7.624235 
 1985 8.936002 
 1986 8.602181 
 1987 8.837496 
 1988 8.455112 
 1989 8.394815 
 1990 8.670464 
 1991  8.55105 
 1992 8.171697 
 1993 8.704752 
 1994 8.787654 
 1995 8.104265 
 1996 8.482878 
 1997 8.732042 
 1998 9.154394 
 1999 8.743619 
 2000 8.358543 
 2001 8.786285 
 2002 8.486434 
 2003 8.754019 
 2004 8.914956 
 2005 8.890953 
 2006 8.889666 
 2007 7.906222 
 2008 8.683644 
 2009 9.050136 
 2010 8.325049 
 2011  8.60692 
 2012 8.534915 
 2013 9.066079 
 2014 9.216141 
 2015 9.106602 
 2016 8.890934 
 2017 9.258688 
 2018 8.480912