# year    value 
 1901 8.302142 
 1902 8.275435 
 1903  7.49648 
 1904 7.954958 
 1905 7.025677 
 1906 7.922924 
 1907  7.48732 
 1908 7.980554 
 1909 8.161691 
 1910 7.749381 
 1911 7.847865 
 1912 8.046897 
 1913 7.453335 
 1914 8.043348 
 1915  8.37906 
 1916 8.372744 
 1917 7.839719 
 1918 7.899427 
 1919 8.271806 
 1920 7.472829 
 1921 8.388745 
 1922  8.63538 
 1923 8.513116 
 1924 8.205371 
 1925 8.161484 
 1926 7.996202 
 1927 7.734726 
 1928 8.530224 
 1929 8.739595 
 1930 8.185935 
 1931 8.455949 
 1932 8.623214 
 1933 8.101548 
 1934 7.759624 
 1935 8.364486 
 1936 7.661926 
 1937 7.922339 
 1938 8.924715 
 1939 7.786716 
 1940  8.00635 
 1941 9.248192 
 1942 8.895517 
 1943 8.119611 
 1944 8.655746 
 1945 8.425178 
 1946 8.800988 
 1947  9.09891 
 1948 8.479224 
 1949 8.227765 
 1950 8.177038 
 1951 7.538402 
 1952   8.3338 
 1953 8.613008 
 1954 8.092282 
 1955 7.905166 
 1956 8.535709 
 1957 7.494025 
 1958  8.78013 
 1959 8.245628 
 1960 7.774426 
 1961 8.460441 
 1962 8.088922 
 1963 8.342877 
 1964 8.500072 
 1965 7.853518 
 1966 8.341908 
 1967 7.888916 
 1968 7.937885 
 1969    8.704 
 1970 7.850946 
 1971  8.38349 
 1972 8.313238 
 1973 8.694454 
 1974   8.5126 
 1975 8.170909 
 1976 7.670301 
 1977 8.420631 
 1978 8.491789 
 1979 8.148133 
 1980 8.490002 
 1981 8.817427 
 1982 8.125763 
 1983 7.746233 
 1984 8.605283 
 1985 8.376335 
 1986 7.994705 
 1987 8.370489 
 1988 8.291716 
 1989 8.145194 
 1990 8.085052 
 1991 8.235326 
 1992 8.180412 
 1993  8.10266 
 1994 8.566599 
 1995 8.437458 
 1996 8.130445 
 1997 8.627814 
 1998 8.991094 
 1999 9.102165 
 2000  9.04108 
 2001 9.045539 
 2002 9.157207 
 2003 8.476205 
 2004 9.668484 
 2005 8.935918 
 2006 9.191607 
 2007 9.518121 
 2008 9.750817 
 2009 9.350543 
 2010 9.285879 
 2011  8.78784 
 2012 9.065395 
 2013 9.451399 
 2014 8.741123 
 2015 9.246153 
 2016 9.610161 
 2017 9.063374 
 2018 9.845124