# year value 1901 20.04941 1902 19.94414 1903 19.68928 1904 19.67489 1905 19.69715 1906 19.85711 1907 19.54645 1908 19.69325 1909 19.59865 1910 19.54029 1911 19.52531 1912 19.93591 1913 20.04343 1914 19.86545 1915 19.93333 1916 19.58909 1917 19.48925 1918 19.70263 1919 20.03808 1920 19.81635 1921 19.44807 1922 19.59086 1923 19.6395 1924 19.65976 1925 19.86601 1926 20.1657 1927 19.84326 1928 19.6869 1929 19.9026 1930 19.9065 1931 19.64318 1932 19.94799 1933 19.73981 1934 19.60337 1935 19.90332 1936 19.91524 1937 20.01014 1938 19.79019 1939 19.95461 1940 20.03155 1941 20.074 1942 19.84415 1943 20.1099 1944 20.33989 1945 20.31876 1946 19.91101 1947 19.80573 1948 19.82989 1949 19.60266 1950 19.53835 1951 19.7351 1952 19.6155 1953 19.89098 1954 19.52882 1955 19.39505 1956 19.06128 1957 19.68446 1958 19.90827 1959 19.63285 1960 19.69573 1961 20.16465 1962 19.88622 1963 20.08225 1964 19.73731 1965 20.09772 1966 19.95892 1967 19.98046 1968 19.90998 1969 20.46299 1970 20.13386 1971 19.63266 1972 20.08723 1973 19.71513 1974 19.35284 1975 19.52142 1976 19.4327 1977 19.85554 1978 19.75984 1979 19.73411 1980 19.9629 1981 19.70309 1982 19.95358 1983 20.10446 1984 19.57122 1985 19.85999 1986 19.94643 1987 20.27297 1988 19.89423 1989 19.86916 1990 19.84993 1991 20.03533 1992 19.94382 1993 19.9648 1994 20.32873 1995 20.15625 1996 19.80836 1997 20.41166 1998 20.31798 1999 19.64775 2000 19.73729 2001 19.93387 2002 20.05278 2003 20.10545 2004 20.16056 2005 19.98792 2006 20.22546 2007 19.64512 2008 19.94315 2009 20.24658 2010 20.0948 2011 20.03436 2012 20.27954 2013 20.082 2014 20.33793 2015 20.64013 2016 20.3109 2017 20.41065 2018 20.08675