# year    value 
 1901 8.213142 
 1902  8.11111 
 1903 8.161609 
 1904 8.037002 
 1905 8.471277 
 1906  8.23671 
 1907 8.030488 
 1908 7.985552 
 1909 8.586361 
 1910  7.88498 
 1911 7.846523 
 1912 7.759681 
 1913 8.064311 
 1914 8.053329 
 1915 8.792081 
 1916 7.927502 
 1917 8.006371 
 1918 8.037469 
 1919 7.983717 
 1920 8.384778 
 1921 7.942637 
 1922 8.298627 
 1923 8.169891 
 1924 8.233614 
 1925 8.453535 
 1926 8.110733 
 1927 8.557748 
 1928 8.138439 
 1929 8.106946 
 1930 8.132139 
 1931 8.295633 
 1932  8.34459 
 1933 8.330624 
 1934 7.701524 
 1935 8.458553 
 1936 8.737872 
 1937 8.076438 
 1938 8.328997 
 1939 8.463638 
 1940 8.667054 
 1941 8.763966 
 1942 8.972574 
 1943 8.428862 
 1944 8.224996 
 1945 8.988332 
 1946 8.821659 
 1947 8.572115 
 1948 8.123465 
 1949 7.997745 
 1950 7.572735 
 1951 8.705968 
 1952 8.052571 
 1953 8.183571 
 1954 8.256089 
 1955 8.333467 
 1956 8.005866 
 1957 7.978321 
 1958 8.272609 
 1959 8.340453 
 1960 8.103032 
 1961 8.202079 
 1962  7.85712 
 1963 8.509618 
 1964 8.280765 
 1965 8.350205 
 1966 7.737565 
 1967 7.456733 
 1968 8.133928 
 1969  8.19644 
 1970 8.089712 
 1971 8.195147 
 1972 8.033683 
 1973  8.29965 
 1974 8.398246 
 1975 8.428273 
 1976 7.850592 
 1977 8.699667 
 1978 8.399756 
 1979 8.267105 
 1980 8.887056 
 1981 7.826676 
 1982  8.35591 
 1983 8.821888 
 1984 8.157285 
 1985 8.049422 
 1986 8.009146 
 1987 8.543571 
 1988 8.795002 
 1989 8.668389 
 1990 9.042383 
 1991 8.286862 
 1992 7.849856 
 1993 8.135681 
 1994 8.516854 
 1995   8.8009 
 1996 8.392829 
 1997 7.972633 
 1998 9.577878 
 1999  9.18451 
 2000 8.324039 
 2001 9.157954 
 2002 8.705742 
 2003 8.941651 
 2004 8.618276 
 2005 9.254302 
 2006 9.519469 
 2007 8.927238 
 2008  9.06284 
 2009 8.974751 
 2010 9.238266 
 2011 9.159009 
 2012 8.424299 
 2013 8.929507 
 2014 9.158115 
 2015 9.156549 
 2016 9.168956 
 2017 9.361703 
 2018 8.507871