# year    value 
 1901 5.876101 
 1902 5.396405 
 1903 5.625584 
 1904 6.926314 
 1905 5.865553 
 1906 5.793252 
 1907 5.141313 
 1908 5.666999 
 1909 5.663423 
 1910  5.68469 
 1911 5.975057 
 1912  6.55096 
 1913 6.567914 
 1914 6.586949 
 1915 6.154731 
 1916 6.883258 
 1917 5.156543 
 1918 6.693745 
 1919 5.047642 
 1920 8.267008 
 1921 6.759158 
 1922 6.608906 
 1923 6.517341 
 1924 6.484081 
 1925 5.596631 
 1926 6.320748 
 1927 6.952464 
 1928 5.561301 
 1929 5.530902 
 1930  6.55645 
 1931 5.619412 
 1932 4.848841 
 1933 5.914867 
 1934  7.80547 
 1935 5.028081 
 1936 6.961545 
 1937 6.662475 
 1938 5.593774 
 1939 5.228462 
 1940 5.896594 
 1941  5.01085 
 1942 6.393814 
 1943 7.557884 
 1944 5.661778 
 1945 8.110991 
 1946 8.024282 
 1947 8.037274 
 1948 7.989315 
 1949 6.461244 
 1950 7.220476 
 1951 5.889652 
 1952 7.118468 
 1953 7.209339 
 1954 5.902809 
 1955 5.290355 
 1956 5.593981 
 1957 6.416487 
 1958 5.436491 
 1959 7.520596 
 1960 6.836252 
 1961 7.669073 
 1962 4.968455 
 1963 6.188968 
 1964 6.549118 
 1965 5.517262 
 1966 6.876897 
 1967 6.539495 
 1968 6.959762 
 1969 6.408741 
 1970 4.595905 
 1971 6.175569 
 1972 6.693006 
 1973 5.568515 
 1974  6.48062 
 1975 6.382825 
 1976 5.965513 
 1977 6.687719 
 1978 5.639705 
 1979 6.263535 
 1980 5.034388 
 1981 7.368557 
 1982 6.105238 
 1983 6.840795 
 1984  4.94222 
 1985 6.211272 
 1986 6.827294 
 1987 4.851473 
 1988 6.737193 
 1989 7.745622 
 1990 7.710277 
 1991 6.072333 
 1992 7.339474 
 1993 7.260576 
 1994 7.738591 
 1995 6.426353 
 1996 6.276014 
 1997 7.136886 
 1998 7.142179 
 1999 7.876578 
 2000 8.335958 
 2001 7.933861 
 2002 7.827193 
 2003  8.03212 
 2004 6.381857 
 2005 7.049664 
 2006  6.68971 
 2007 9.004604 
 2008 7.290442 
 2009 8.443166 
 2010 6.822637 
 2011 8.754848 
 2012 8.299072 
 2013 6.474652 
 2014 8.346631 
 2015 7.871954 
 2016 7.352166 
 2017 8.529776 
 2018  8.65164