# year    value 
 1901 3.890296 
 1902 3.071072 
 1903 2.871518 
 1904  3.14876 
 1905 2.724477 
 1906 3.559111 
 1907 3.112584 
 1908 3.010453 
 1909 2.859803 
 1910 3.434485 
 1911 3.006317 
 1912 2.947171 
 1913  2.93092 
 1914 3.641606 
 1915 3.471565 
 1916 3.222554 
 1917 2.949033 
 1918 3.327353 
 1919 3.081602 
 1920 3.379614 
 1921 3.352925 
 1922 3.354375 
 1923 3.435848 
 1924 3.180785 
 1925 3.642617 
 1926  3.84503 
 1927 3.195617 
 1928 3.377191 
 1929 3.619226 
 1930 3.581962 
 1931 3.289417 
 1932 3.417408 
 1933 2.791591 
 1934 3.684198 
 1935 3.002646 
 1936 3.175218 
 1937  2.95428 
 1938  4.11356 
 1939 3.632974 
 1940 3.943454 
 1941 3.844337 
 1942  3.55045 
 1943 3.719543 
 1944  3.92905 
 1945 3.691177 
 1946 3.747668 
 1947 4.420666 
 1948  3.79023 
 1949 3.554258 
 1950 3.578239 
 1951 3.255715 
 1952 3.407763 
 1953 3.823433 
 1954 2.964016 
 1955 2.726448 
 1956 3.153701 
 1957 3.081379 
 1958 3.558312 
 1959 3.974713 
 1960 2.995832 
 1961 4.071205 
 1962 3.660244 
 1963  3.62723 
 1964 3.361255 
 1965 3.256759 
 1966 3.503824 
 1967 3.529098 
 1968 4.172691 
 1969 3.489434 
 1970 3.173457 
 1971 3.450247 
 1972 3.856595 
 1973 3.624975 
 1974  3.69401 
 1975 3.629177 
 1976 3.019148 
 1977 3.912823 
 1978 3.994221 
 1979  3.70475 
 1980 3.224165 
 1981 4.589611 
 1982 3.649851 
 1983 3.639187 
 1984 3.741466 
 1985 3.797276 
 1986 3.953931 
 1987  3.55773 
 1988 3.850679 
 1989 4.561882 
 1990 4.717428 
 1991 3.559866 
 1992 4.171829 
 1993 4.081055 
 1994 4.503871 
 1995 3.923301 
 1996 3.844841 
 1997 4.596694 
 1998 4.590078 
 1999 4.054566 
 2000 4.986522 
 2001 4.828666 
 2002 4.614982 
 2003 4.167007 
 2004 4.955837 
 2005 4.575934 
 2006 4.557072 
 2007 5.074448 
 2008 5.367142 
 2009  4.78525 
 2010 4.096744 
 2011 4.486911 
 2012 4.702945 
 2013  4.77609 
 2014  5.02361 
 2015 5.093592 
 2016 5.456101 
 2017 5.399142 
 2018 5.606958