# year    value 
 1901 17.58468 
 1902 17.02797 
 1903 17.02127 
 1904 17.34171 
 1905 17.26877 
 1906 16.74507 
 1907 16.68933 
 1908  17.1534 
 1909 16.93713 
 1910 17.11485 
 1911 16.66291 
 1912 16.67019 
 1913 17.41998 
 1914 17.52827 
 1915 17.00153 
 1916 16.01958 
 1917 16.67073 
 1918 17.24893 
 1919 16.91798 
 1920 16.45068 
 1921 16.05379 
 1922 16.72359 
 1923 16.70641 
 1924 16.69702 
 1925 16.93602 
 1926 17.29534 
 1927 16.77424 
 1928 16.69973 
 1929 16.85472 
 1930 17.11384 
 1931 16.61215 
 1932 17.27357 
 1933 16.71968 
 1934 17.24771 
 1935 17.15335 
 1936  16.9653 
 1937 17.50316 
 1938 16.87046 
 1939 17.80008 
 1940 17.62009 
 1941 17.53654 
 1942 16.56519 
 1943 17.12396 
 1944 17.87472 
 1945 17.65752 
 1946  16.8572 
 1947 16.85415 
 1948 17.08393 
 1949 16.65853 
 1950 17.01552 
 1951 17.47557 
 1952 16.35658 
 1953 16.96409 
 1954 16.61334 
 1955 16.38026 
 1956  16.2455 
 1957 16.59085 
 1958 17.43838 
 1959 17.03766 
 1960 16.86834 
 1961 17.51075 
 1962 16.57376 
 1963  17.8249 
 1964  16.6992 
 1965 17.77382 
 1966 17.13925 
 1967 16.66743 
 1968 17.59941 
 1969 17.40482 
 1970 17.10209 
 1971 16.89095 
 1972 17.47347 
 1973 16.59403 
 1974 16.74722 
 1975 16.70033 
 1976 16.76801 
 1977 17.17827 
 1978 16.85558 
 1979 17.38309 
 1980 16.94185 
 1981 16.75339 
 1982 17.30581 
 1983 16.68983 
 1984 16.38016 
 1985 17.00362 
 1986  17.3533 
 1987 17.67411 
 1988 16.70467 
 1989 17.13615 
 1990 16.90726 
 1991  17.1722 
 1992 17.05424 
 1993 17.22546 
 1994 17.57808 
 1995 17.33787 
 1996 16.89157 
 1997 17.98031 
 1998 17.79044 
 1999 16.75402 
 2000 16.80679 
 2001 17.28338 
 2002 17.03572 
 2003  17.0714 
 2004 17.24038 
 2005 17.48178 
 2006 17.79976 
 2007 16.26886 
 2008 17.37173 
 2009 17.32576 
 2010 16.94215 
 2011 17.31109 
 2012 17.36091 
 2013 17.08756 
 2014 17.86418 
 2015   18.296 
 2016 17.43084 
 2017 17.86976 
 2018 16.61736