# year value 1901 19.89526 1902 20.26525 1903 19.56688 1904 19.68988 1905 19.56427 1906 20.31048 1907 19.4338 1908 19.67569 1909 19.6038 1910 19.18611 1911 19.36858 1912 20.09266 1913 19.94954 1914 19.70756 1915 20.06798 1916 19.92908 1917 19.35912 1918 19.4971 1919 20.4199 1920 20.10165 1921 19.80658 1922 19.59383 1923 19.62883 1924 19.63927 1925 19.85023 1926 20.02793 1927 19.75726 1928 19.74942 1929 19.77417 1930 19.93213 1931 19.42304 1932 19.66121 1933 19.85067 1934 19.47878 1935 20.11267 1936 19.98486 1937 19.72174 1938 19.44409 1939 19.62135 1940 20.02242 1941 19.8 1942 19.60613 1943 19.92279 1944 19.83737 1945 20.15767 1946 19.88066 1947 19.8579 1948 19.5121 1949 19.65541 1950 19.51405 1951 19.44704 1952 20.00551 1953 19.80678 1954 19.32258 1955 19.03789 1956 18.79995 1957 20.0125 1958 19.67073 1959 19.26879 1960 19.35666 1961 20.05423 1962 19.76248 1963 19.95429 1964 19.71803 1965 19.67338 1966 20.04281 1967 20.35462 1968 19.09204 1969 20.74924 1970 20.32 1971 19.23324 1972 19.91787 1973 20.00651 1974 19.49266 1975 19.56773 1976 19.00074 1977 19.64122 1978 19.7179 1979 19.49328 1980 20.35009 1981 20.17459 1982 19.86266 1983 20.44707 1984 19.63855 1985 19.98733 1986 19.84392 1987 19.95031 1988 19.68665 1989 19.45518 1990 19.7053 1991 20.46238 1992 20.42511 1993 20.19191 1994 20.40805 1995 19.95997 1996 19.98081 1997 20.45505 1998 20.43583 1999 19.4044 2000 19.72006 2001 19.6865 2002 20.18869 2003 20.0147 2004 19.94737 2005 19.93885 2006 19.90422 2007 19.48298 2008 19.48886 2009 20.57006 2010 20.23411 2011 19.84068 2012 20.18362 2013 19.94894 2014 19.90318 2015 20.75184 2016 20.02966 2017 20.23238 2018 20.51689