# year    value 
 1901 8.895712 
 1902 8.529156 
 1903 9.799192 
 1904 8.386692 
 1905 8.473992 
 1906 9.885094 
 1907 10.41607 
 1908 8.152649 
 1909 9.168415 
 1910 8.577126 
 1911 10.52117 
 1912 6.800136 
 1913 10.24073 
 1914  8.55025 
 1915  7.28371 
 1916 8.977188 
 1917 9.519913 
 1918  9.02115 
 1919 8.376187 
 1920 8.560772 
 1921 9.571551 
 1922 7.451328 
 1923 10.21071 
 1924 9.584872 
 1925 8.616629 
 1926  11.4817 
 1927  9.79272 
 1928 10.00772 
 1929  10.7087 
 1930 10.32922 
 1931 8.244491 
 1932 10.77571 
 1933 9.386616 
 1934 9.987744 
 1935 10.19506 
 1936 8.287317 
 1937 9.437068 
 1938 10.32789 
 1939 9.418343 
 1940 9.866524 
 1941 8.210192 
 1942 10.92867 
 1943 10.30145 
 1944 9.104512 
 1945 9.501699 
 1946  9.52327 
 1947 10.92886 
 1948 10.11875 
 1949 11.03137 
 1950 9.532783 
 1951 10.54467 
 1952  8.31774 
 1953 10.33011 
 1954 9.964884 
 1955 9.115635 
 1956 9.051572 
 1957  9.70015 
 1958  10.3688 
 1959  9.46171 
 1960 9.889373 
 1961 11.17575 
 1962 9.505005 
 1963  10.8603 
 1964 9.822607 
 1965 9.067101 
 1966 10.28496 
 1967 10.59899 
 1968 10.04738 
 1969 10.51276 
 1970 10.23547 
 1971 9.013607 
 1972 8.241892 
 1973 9.409655 
 1974 8.412488 
 1975 9.804946 
 1976 9.603439 
 1977 9.738956 
 1978 8.867695 
 1979 9.713949 
 1980 9.328051 
 1981 9.856015 
 1982 11.11017 
 1983 9.752437 
 1984 10.18144 
 1985 9.663824 
 1986 10.36661 
 1987 11.26677 
 1988 9.484992 
 1989 9.629864 
 1990 10.10757 
 1991 10.11968 
 1992 10.06691 
 1993 8.949494 
 1994 10.83189 
 1995 9.834179 
 1996 9.355717 
 1997 10.35517 
 1998 9.196169 
 1999 10.48063 
 2000 11.26851 
 2001 9.883273 
 2002 10.47722 
 2003 9.958981 
 2004 10.82303 
 2005 10.54179 
 2006 12.38495 
 2007 9.069029 
 2008 10.16405 
 2009 11.21216 
 2010 9.734923 
 2011 11.32256 
 2012 11.30151 
 2013 10.89056 
 2014 12.11742 
 2015 10.73253 
 2016 10.77444 
 2017 10.05856 
 2018 12.05992