# year    value 
 1901 8.172047 
 1902 7.851061 
 1903 8.061607 
 1904  8.49226 
 1905 8.861994 
 1906 8.293239 
 1907 7.890419 
 1908 8.152718 
 1909   9.0086 
 1910 8.093151 
 1911 8.268565 
 1912 7.621384 
 1913 8.778308 
 1914 8.242088 
 1915 8.412766 
 1916 8.195586 
 1917 8.659812 
 1918 8.547206 
 1919 8.086069 
 1920 8.060671 
 1921 8.268176 
 1922 8.533241 
 1923 9.258278 
 1924 8.820415 
 1925   8.5144 
 1926  8.55547 
 1927 9.060302 
 1928 8.669808 
 1929 8.652886 
 1930 8.772675 
 1931 9.174893 
 1932 8.711884 
 1933 8.566148 
 1934 8.871892 
 1935 8.371002 
 1936 8.705907 
 1937 8.907025 
 1938 9.447883 
 1939 8.508917 
 1940 8.788068 
 1941 8.244494 
 1942 8.806507 
 1943 8.731832 
 1944  8.76924 
 1945 8.641493 
 1946 8.581186 
 1947 9.163474 
 1948 9.061222 
 1949 8.672123 
 1950 8.190065 
 1951 8.285779 
 1952 8.180601 
 1953 8.653312 
 1954 9.285364 
 1955  8.77306 
 1956 8.264518 
 1957 8.726694 
 1958 8.658547 
 1959 7.815091 
 1960 8.563722 
 1961 8.683294 
 1962 8.773641 
 1963 9.724851 
 1964 8.484097 
 1965 8.301367 
 1966 8.536342 
 1967 8.917486 
 1968 8.479618 
 1969 8.565525 
 1970 8.648639 
 1971 9.313684 
 1972 8.000772 
 1973  8.66046 
 1974 8.495085 
 1975 8.811929 
 1976 7.374564 
 1977 9.030889 
 1978 8.763793 
 1979  8.82481 
 1980 8.842969 
 1981  8.86482 
 1982 8.838996 
 1983 9.396235 
 1984 8.414837 
 1985 8.214926 
 1986 8.264636 
 1987 8.378236 
 1988 8.939211 
 1989 8.856949 
 1990 9.370896 
 1991 9.010017 
 1992 8.395084 
 1993 7.561959 
 1994 9.687849 
 1995 9.165331 
 1996 8.372072 
 1997  8.88966 
 1998 9.209154 
 1999 9.427036 
 2000 8.583102 
 2001  9.68631 
 2002 9.028738 
 2003 9.330294 
 2004 9.858557 
 2005 10.21015 
 2006 9.618731 
 2007  9.56693 
 2008 9.733137 
 2009 9.575927 
 2010 9.924667 
 2011 9.596074 
 2012 9.622538 
 2013 9.838007 
 2014 9.092683 
 2015 9.842275 
 2016  9.44607 
 2017 9.702515 
 2018 9.238229