# year    value 
 1901 6.375227 
 1902 5.560285 
 1903 5.488005 
 1904 5.350909 
 1905  5.24968 
 1906 6.111496 
 1907 5.236229 
 1908 5.237313 
 1909 5.127434 
 1910 6.136181 
 1911 5.545732 
 1912 5.325306 
 1913  5.52068 
 1914 6.069451 
 1915 5.865702 
 1916 5.482851 
 1917 5.200152 
 1918 5.651016 
 1919 5.386801 
 1920 6.049277 
 1921 6.200729 
 1922 6.111384 
 1923 5.408839 
 1924 5.456945 
 1925  6.15124 
 1926 5.824689 
 1927 5.743186 
 1928 5.376681 
 1929 5.746509 
 1930 6.177314 
 1931 5.648497 
 1932 5.699276 
 1933 5.401896 
 1934 5.952737 
 1935 5.513548 
 1936 5.608973 
 1937  5.57282 
 1938 6.618857 
 1939 5.910786 
 1940 6.062957 
 1941 5.987055 
 1942  5.87625 
 1943 6.020254 
 1944  6.38421 
 1945 6.022736 
 1946 6.356928 
 1947 6.299747 
 1948 6.110229 
 1949 5.906622 
 1950 5.923794 
 1951  5.99591 
 1952 5.753624 
 1953 6.304382 
 1954 5.132655 
 1955 5.454151 
 1956 5.243161 
 1957 5.644183 
 1958 5.875163 
 1959 6.379075 
 1960 5.132816 
 1961 6.613237 
 1962 6.337111 
 1963 6.044053 
 1964 5.584547 
 1965 5.642277 
 1966 6.091461 
 1967 6.143003 
 1968 6.751471 
 1969 5.492181 
 1970 5.733493 
 1971 5.740335 
 1972 6.075846 
 1973 6.410156 
 1974 6.054428 
 1975 6.339484 
 1976 5.642498 
 1977  7.09819 
 1978 6.257875 
 1979 6.026978 
 1980 5.742509 
 1981 6.935093 
 1982 6.135465 
 1983 6.263051 
 1984 6.103519 
 1985 6.264677 
 1986 6.646356 
 1987 6.075496 
 1988 6.483475 
 1989 6.789474 
 1990 7.274109 
 1991 6.490553 
 1992 6.379988 
 1993 6.430409 
 1994 6.808729 
 1995 6.667002 
 1996 5.823996 
 1997 6.772082 
 1998 7.057596 
 1999 6.737367 
 2000 7.584797 
 2001 7.528393 
 2002 6.845772 
 2003 6.510767 
 2004 7.177596 
 2005 7.084811 
 2006 7.339467 
 2007   7.5045 
 2008 7.689529 
 2009 7.013508 
 2010 7.089259 
 2011 6.938289 
 2012 7.792279 
 2013 6.931713 
 2014 7.282174 
 2015 7.486171 
 2016 7.994559 
 2017  7.70393 
 2018 7.554878