# year    value 
 1901 7.730722 
 1902 7.499182 
 1903 7.605613 
 1904 7.291342 
 1905 7.280294 
 1906 7.891277 
 1907 7.383071 
 1908 8.010405 
 1909 7.816856 
 1910 7.901369 
 1911  7.82736 
 1912 7.328537 
 1913 7.647329 
 1914 8.113548 
 1915 7.925924 
 1916 7.559788 
 1917 7.662501 
 1918 7.422113 
 1919 7.481405 
 1920 7.678711 
 1921 8.011973 
 1922 7.566463 
 1923 8.020669 
 1924 7.598803 
 1925  7.60777 
 1926  8.19986 
 1927 8.162237 
 1928 7.787895 
 1929 7.602564 
 1930   8.1777 
 1931  7.86144 
 1932 7.761694 
 1933 7.518936 
 1934 7.943127 
 1935 7.810789 
 1936   8.5762 
 1937 7.911471 
 1938  8.04096 
 1939 7.906205 
 1940 7.985782 
 1941 8.414071 
 1942 7.874301 
 1943 7.904025 
 1944 7.897875 
 1945 7.982477 
 1946 7.800935 
 1947 7.597094 
 1948 7.932481 
 1949 7.330299 
 1950 7.651585 
 1951 7.844256 
 1952 7.991479 
 1953 8.482193 
 1954  8.33943 
 1955 7.666032 
 1956 7.856318 
 1957 8.375231 
 1958 8.182389 
 1959 8.008961 
 1960 8.028475 
 1961 7.655242 
 1962 7.984971 
 1963 7.426461 
 1964 7.761499 
 1965 7.182733 
 1966 7.770737 
 1967 7.956572 
 1968 7.789085 
 1969 8.184538 
 1970 7.601008 
 1971 8.283583 
 1972  7.63314 
 1973 8.095337 
 1974 7.958658 
 1975 8.078297 
 1976 7.793155 
 1977 8.225087 
 1978 7.706243 
 1979 7.832481 
 1980 8.301144 
 1981 8.035849 
 1982 7.869842 
 1983  8.28119 
 1984 7.960998 
 1985 7.675438 
 1986 7.876569 
 1987 7.822017 
 1988 8.364345 
 1989 8.374741 
 1990 8.836219 
 1991  8.99012 
 1992 7.769661 
 1993 8.371855 
 1994 8.590878 
 1995 8.678571 
 1996 7.887885 
 1997 8.934085 
 1998 8.874684 
 1999 8.220407 
 2000 8.256161 
 2001  8.89238 
 2002 8.955803 
 2003 8.962397 
 2004 8.651556 
 2005 8.866697 
 2006 8.811387 
 2007 9.225082 
 2008 8.589622 
 2009 8.765306 
 2010 9.032208 
 2011 8.970676 
 2012  8.77796 
 2013 9.035367 
 2014 8.929162 
 2015 8.962414 
 2016 9.378416 
 2017 8.918233 
 2018 8.873106