# year value 1901 3.711655 1902 3.464962 1903 3.339546 1904 3.497123 1905 3.364703 1906 3.555612 1907 3.249976 1908 3.372539 1909 3.269918 1910 3.44397 1911 3.265388 1912 3.109833 1913 3.271889 1914 3.769051 1915 3.591292 1916 3.305822 1917 3.379403 1918 3.492021 1919 3.341107 1920 3.336715 1921 3.684455 1922 3.39072 1923 3.556346 1924 3.552065 1925 3.861129 1926 3.973086 1927 3.64915 1928 3.561129 1929 3.195165 1930 3.57235 1931 3.491507 1932 3.786688 1933 3.347099 1934 3.870473 1935 3.542523 1936 3.55074 1937 3.449607 1938 3.903085 1939 4.094239 1940 3.938134 1941 3.951241 1942 3.754973 1943 3.925571 1944 3.720346 1945 3.650581 1946 3.932252 1947 3.790017 1948 3.942943 1949 3.64045 1950 3.474701 1951 3.613324 1952 3.519251 1953 3.985754 1954 3.477062 1955 3.691638 1956 3.195814 1957 3.408551 1958 4.106762 1959 3.804071 1960 3.677179 1961 3.9639 1962 3.914214 1963 4.116386 1964 3.366743 1965 3.525913 1966 3.787699 1967 3.600354 1968 3.652359 1969 3.248965 1970 3.680327 1971 3.766044 1972 3.34103 1973 3.896538 1974 3.507316 1975 3.802161 1976 3.433858 1977 3.852832 1978 3.941199 1979 4.004013 1980 3.893517 1981 4.218308 1982 3.78981 1983 4.01676 1984 3.523589 1985 3.618359 1986 4.053373 1987 4.034452 1988 4.339038 1989 4.315515 1990 4.584019 1991 4.106802 1992 4.041449 1993 3.918244 1994 4.509593 1995 4.551705 1996 3.996416 1997 4.396903 1998 4.783379 1999 4.736722 2000 4.370972 2001 4.671387 2002 4.744669 2003 4.602963 2004 4.764667 2005 4.486715 2006 4.781437 2007 5.067226 2008 4.712748 2009 4.539443 2010 4.65297 2011 4.488928 2012 4.419275 2013 4.765692 2014 4.867874 2015 5.267933 2016 5.091512 2017 5.168514 2018 5.070175