# year    value 
 1901 22.82815 
 1902 21.53992 
 1903 21.12515 
 1904 21.12821 
 1905  21.6394 
 1906 21.28217 
 1907 21.36174 
 1908 21.26637 
 1909 22.49166 
 1910 22.36228 
 1911 22.18168 
 1912 21.35533 
 1913 22.53351 
 1914   22.398 
 1915 20.46674 
 1916  22.0159 
 1917  22.0327 
 1918 22.88793 
 1919 22.52054 
 1920 21.69204 
 1921 22.73325 
 1922 22.73079 
 1923 22.22568 
 1924 21.84641 
 1925  22.4703 
 1926 22.16599 
 1927 21.34272 
 1928 21.37187 
 1929 22.59866 
 1930 22.93246 
 1931 23.23078 
 1932  22.7323 
 1933 23.51203 
 1934 23.85194 
 1935 22.72732 
 1936 24.36271 
 1937 23.43062 
 1938 22.94261 
 1939 22.82583 
 1940 22.70577 
 1941  22.2465 
 1942 22.00488 
 1943 22.81987 
 1944 21.92231 
 1945 21.56786 
 1946 22.54069 
 1947 22.51126 
 1948 22.44385 
 1949 22.54312 
 1950 21.25652 
 1951 21.66812 
 1952 22.99574 
 1953 22.85104 
 1954 22.93985 
 1955 22.51007 
 1956 22.98996 
 1957  22.6887 
 1958 22.35815 
 1959 22.93097 
 1960 22.62769 
 1961 22.87769 
 1962 21.99931 
 1963 23.02606 
 1964 22.51652 
 1965  21.9451 
 1966 22.45099 
 1967 21.89368 
 1968 21.79114 
 1969 22.39662 
 1970  23.0891 
 1971 22.46196 
 1972 22.13961 
 1973 22.49371 
 1974 22.38271 
 1975 22.11362 
 1976 22.33959 
 1977 22.86616 
 1978 22.63836 
 1979 22.11055 
 1980 23.33783 
 1981 22.69914 
 1982 22.01104 
 1983 23.05192 
 1984 22.92796 
 1985 22.15072 
 1986 22.65052 
 1987 22.36788 
 1988 23.57575 
 1989 22.35032 
 1990 22.83199 
 1991  22.7633 
 1992 21.03494 
 1993 21.56422 
 1994 22.99723 
 1995 22.70096 
 1996 22.89127 
 1997 22.28646 
 1998 22.84924 
 1999 22.30641 
 2000 22.83927 
 2001  23.2994 
 2002 23.20334 
 2003 23.28075 
 2004 21.47758 
 2005 22.86523 
 2006 23.82685 
 2007 23.24928 
 2008 22.71634 
 2009 22.16189 
 2010 23.09404 
 2011 23.87691 
 2012 24.04769 
 2013 23.19908 
 2014 22.65248 
 2015 23.29115 
 2016 23.50011 
 2017 22.96692 
 2018 23.62167