# year value 1901 19.7793 1902 19.78894 1903 19.54505 1904 19.54885 1905 19.56105 1906 19.66819 1907 19.60581 1908 19.72017 1909 19.67907 1910 19.55222 1911 19.60373 1912 19.52097 1913 19.43043 1914 19.63659 1915 19.83982 1916 19.71531 1917 19.49463 1918 19.54398 1919 19.68554 1920 19.59997 1921 19.78862 1922 19.83262 1923 19.771 1924 19.83331 1925 19.60044 1926 19.8503 1927 19.8446 1928 19.95117 1929 19.71773 1930 19.70076 1931 19.9189 1932 19.76709 1933 19.88277 1934 19.78398 1935 19.90184 1936 19.78529 1937 19.91476 1938 19.84318 1939 19.85082 1940 19.93726 1941 20.18359 1942 20.02865 1943 19.76587 1944 19.79677 1945 19.804 1946 20.08652 1947 20.02687 1948 19.82501 1949 19.70938 1950 19.62325 1951 19.86688 1952 19.94047 1953 20.03777 1954 19.8562 1955 19.71785 1956 19.58289 1957 19.73558 1958 20.05033 1959 19.82564 1960 19.9144 1961 19.70278 1962 19.69162 1963 19.83334 1964 19.60584 1965 19.67045 1966 19.8771 1967 19.4751 1968 19.48339 1969 19.98691 1970 19.74584 1971 19.45872 1972 19.8005 1973 19.96557 1974 19.59013 1975 19.65199 1976 19.56989 1977 19.85546 1978 19.87376 1979 20.02618 1980 20.1357 1981 19.8903 1982 19.85074 1983 19.93025 1984 19.78225 1985 19.82801 1986 19.84779 1987 20.19812 1988 20.09091 1989 19.79413 1990 20.13201 1991 20.07195 1992 19.75656 1993 19.99561 1994 20.16754 1995 20.18402 1996 20.07678 1997 20.05903 1998 20.68103 1999 20.27026 2000 20.13733 2001 20.36044 2002 20.49706 2003 20.50195 2004 20.35605 2005 20.48141 2006 20.52677 2007 20.37329 2008 20.18721 2009 20.72583 2010 20.68428 2011 20.37556 2012 20.44434 2013 20.46788 2014 20.4854 2015 20.69613 2016 20.85143 2017 20.67824 2018 20.55476