# year    value 
 1901 8.318085 
 1902 7.791359 
 1903  7.68259 
 1904 7.872631 
 1905  7.62208 
 1906 8.180911 
 1907 7.749514 
 1908 7.783143 
 1909 7.600505 
 1910 7.837203 
 1911 7.613855 
 1912 7.826489 
 1913  7.72767 
 1914 8.035045 
 1915 8.143493 
 1916 7.884728 
 1917 7.682142 
 1918 7.774231 
 1919 7.879996 
 1920 7.932877 
 1921 8.018132 
 1922 7.990681 
 1923 8.043162 
 1924 7.990243 
 1925  8.12421 
 1926 8.414931 
 1927 7.872448 
 1928 8.137199 
 1929 8.100011 
 1930  8.11269 
 1931 7.936713 
 1932 8.157249 
 1933 7.763106 
 1934 8.183907 
 1935 7.866163 
 1936 7.978948 
 1937 7.811145 
 1938 8.542423 
 1939 8.202399 
 1940 8.481022 
 1941 8.410574 
 1942 8.147318 
 1943 8.466258 
 1944 8.380589 
 1945 8.307288 
 1946 8.238578 
 1947 8.704749 
 1948 8.326048 
 1949 8.211803 
 1950 8.039839 
 1951 7.890926 
 1952 8.115989 
 1953 8.518347 
 1954 7.942134 
 1955 7.605851 
 1956 7.792932 
 1957 7.896561 
 1958 8.283324 
 1959 8.347885 
 1960 7.843533 
 1961 8.365089 
 1962 8.234657 
 1963 8.098185 
 1964 7.879389 
 1965 7.979394 
 1966 8.027281 
 1967 8.222233 
 1968 8.386238 
 1969 8.282507 
 1970 8.040546 
 1971 7.958568 
 1972 8.207902 
 1973 8.381272 
 1974 8.187375 
 1975 8.301569 
 1976 7.721377 
 1977 8.349526 
 1978 8.473044 
 1979 8.240499 
 1980 8.215761 
 1981  8.89185 
 1982 8.168846 
 1983 8.403955 
 1984 8.423326 
 1985 8.223839 
 1986 8.384639 
 1987 8.221688 
 1988 8.571279 
 1989  8.74291 
 1990 9.181573 
 1991 8.506152 
 1992 8.654161 
 1993 8.665473 
 1994 8.870536 
 1995 8.668411 
 1996 8.516462 
 1997 8.918065 
 1998 9.113577 
 1999 8.555667 
 2000  9.15688 
 2001 9.039847 
 2002 9.161016 
 2003 8.941149 
 2004 9.179352 
 2005 9.175053 
 2006 8.848988 
 2007 9.317218 
 2008 9.353939 
 2009 9.170661 
 2010 9.065016 
 2011 9.101787 
 2012 9.088073 
 2013 9.136641 
 2014 9.394643 
 2015 9.466345 
 2016 9.847066 
 2017 9.643838 
 2018 9.642357