# year    value 
 1901 7.462442 
 1902 7.110863 
 1903 7.134415 
 1904 7.024854 
 1905 7.180095 
 1906 7.454677 
 1907 6.724104 
 1908 7.022672 
 1909 7.163958 
 1910 7.364782 
 1911 7.148426 
 1912 6.803017 
 1913 7.384842 
 1914 7.481226 
 1915 7.492884 
 1916 7.100038 
 1917 6.841879 
 1918 7.183297 
 1919  7.02862 
 1920  7.23458 
 1921 7.743175 
 1922  7.36671 
 1923 7.420045 
 1924 7.137734 
 1925  7.70434 
 1926 7.374941 
 1927 7.339776 
 1928 7.236142 
 1929 6.769627 
 1930 7.603941 
 1931 7.608025 
 1932 7.615811 
 1933 7.057592 
 1934  7.60275 
 1935 7.374095 
 1936 7.425884 
 1937 7.454975 
 1938 7.953188 
 1939 7.805349 
 1940 7.379977 
 1941 7.386229 
 1942  7.29457 
 1943 7.576873 
 1944 7.806405 
 1945 7.167524 
 1946 7.652607 
 1947  7.45509 
 1948 7.814226 
 1949 7.582438 
 1950 7.052734 
 1951 7.410758 
 1952 7.557795 
 1953 7.880233 
 1954   7.2845 
 1955 7.692761 
 1956 6.924181 
 1957 7.526323 
 1958 7.634132 
 1959 7.470839 
 1960 7.433706 
 1961 7.943321 
 1962 7.762027 
 1963 7.729668 
 1964 7.271167 
 1965  7.28416 
 1966 7.517402 
 1967 7.543394 
 1968 7.434547 
 1969 6.849264 
 1970 7.413425 
 1971   7.6716 
 1972 6.927154 
 1973 7.891288 
 1974 7.388602 
 1975 7.974135 
 1976 7.086544 
 1977 7.830987 
 1978 7.401847 
 1979 7.578394 
 1980 7.489621 
 1981 8.309958 
 1982 7.614538 
 1983 8.213747 
 1984 7.473245 
 1985 7.283332 
 1986  7.77983 
 1987 7.851405 
 1988 8.078787 
 1989 8.106958 
 1990 8.480941 
 1991 8.142026 
 1992 7.776431 
 1993 7.534034 
 1994 8.095788 
 1995 8.438608 
 1996 7.433011 
 1997 8.110359 
 1998 8.670809 
 1999 8.799151 
 2000 8.372135 
 2001 8.623828 
 2002 8.543546 
 2003 8.275359 
 2004 8.470193 
 2005 8.597046 
 2006 8.798794 
 2007 8.847548 
 2008 8.549062 
 2009 8.238297 
 2010 8.623837 
 2011 8.421996 
 2012 8.699711 
 2013 8.540348 
 2014 8.367633 
 2015 9.048279 
 2016 9.100427 
 2017   8.9823 
 2018 8.578012