# year    value 
 1901 7.670718 
 1902 7.763649 
 1903 7.388858 
 1904 7.547442 
 1905 7.315904 
 1906 7.575504 
 1907 7.396062 
 1908 7.587258 
 1909 7.705193 
 1910 7.389611 
 1911   7.4334 
 1912 7.580205 
 1913  7.42212 
 1914 7.778645 
 1915 7.959405 
 1916 7.612758 
 1917 7.509088 
 1918 7.421983 
 1919 7.616137 
 1920 7.449028 
 1921 7.713215 
 1922 7.945808 
 1923 7.793561 
 1924 7.839075 
 1925 7.646317 
 1926 7.814827 
 1927 7.747797 
 1928  7.81244 
 1929 7.584646 
 1930 7.558012 
 1931 7.754346 
 1932 7.882921 
 1933 7.787603 
 1934  7.48495 
 1935 7.746742 
 1936 7.557717 
 1937 7.632992 
 1938 7.898191 
 1939 7.931989 
 1940  8.08038 
 1941 8.571609 
 1942 8.189842 
 1943 7.871346 
 1944 7.776576 
 1945 7.826104 
 1946 8.383825 
 1947 8.113572 
 1948  7.95573 
 1949 7.652853 
 1950 7.387043 
 1951 7.641005 
 1952   7.7427 
 1953    8.072 
 1954 7.493009 
 1955 7.721067 
 1956 7.507176 
 1957 7.281774 
 1958  8.06381 
 1959 7.729593 
 1960 7.773901 
 1961  7.80346 
 1962 7.577292 
 1963 7.847525 
 1964 7.515924 
 1965 7.635653 
 1966 7.905754 
 1967 7.255397 
 1968 7.440287 
 1969 7.631209 
 1970 7.652022 
 1971 7.725242 
 1972 7.600856 
 1973 8.005405 
 1974 7.560916 
 1975  7.69752 
 1976 7.456402 
 1977 7.809226 
 1978 7.879142 
 1979 8.038344 
 1980 8.054808 
 1981 7.948251 
 1982 7.759148 
 1983 7.694877 
 1984 7.606421 
 1985  7.82088 
 1986 7.704868 
 1987 8.219964 
 1988 8.286923 
 1989 7.860822 
 1990 8.230607 
 1991 7.937873 
 1992 7.608016 
 1993 7.780358 
 1994 8.194949 
 1995 8.006186 
 1996  7.81075 
 1997 7.885499 
 1998 8.684696 
 1999 8.698276 
 2000 8.178357 
 2001 8.545136 
 2002 8.595781 
 2003 8.339597 
 2004 8.604324 
 2005 8.388551 
 2006 8.913545 
 2007 8.786337 
 2008 8.371194 
 2009 8.814635 
 2010 8.766771 
 2011 8.344757 
 2012 8.121983 
 2013 8.658505 
 2014 8.339799 
 2015 8.685051 
 2016 8.944216 
 2017 8.836685 
 2018 8.645422