# year value 1901 18.76218 1902 19.1316 1903 18.73115 1904 18.51373 1905 18.51828 1906 18.85388 1907 18.4232 1908 18.60755 1909 18.48669 1910 18.35108 1911 18.30141 1912 18.97494 1913 18.74399 1914 18.7951 1915 19.07592 1916 18.68641 1917 18.31317 1918 18.26268 1919 18.93465 1920 18.68265 1921 18.74364 1922 18.76343 1923 18.8096 1924 18.88453 1925 18.82948 1926 19.06186 1927 18.80812 1928 19.0914 1929 18.57017 1930 18.71588 1931 18.7547 1932 18.76717 1933 18.87676 1934 18.84133 1935 18.71887 1936 18.86191 1937 18.7121 1938 18.81792 1939 18.75308 1940 18.93699 1941 19.20926 1942 18.90845 1943 18.88673 1944 18.79008 1945 18.96278 1946 18.91521 1947 18.87922 1948 18.75863 1949 18.83971 1950 18.55535 1951 18.59647 1952 18.93814 1953 18.89359 1954 18.60775 1955 18.4536 1956 18.40444 1957 18.88547 1958 19.06834 1959 18.88983 1960 18.4384 1961 19.10369 1962 18.65944 1963 18.76649 1964 18.85184 1965 18.68493 1966 18.89479 1967 19.04108 1968 18.20618 1969 19.45875 1970 19.13031 1971 18.6442 1972 18.91988 1973 19.29275 1974 18.53488 1975 18.66845 1976 18.44446 1977 18.89081 1978 18.74099 1979 18.743 1980 19.28587 1981 18.95408 1982 18.77103 1983 19.74078 1984 18.96095 1985 18.97857 1986 19.14396 1987 19.47221 1988 19.22457 1989 18.80829 1990 19.21458 1991 19.33131 1992 19.63907 1993 19.36532 1994 19.35497 1995 19.27248 1996 19.03337 1997 19.15592 1998 19.76059 1999 19.04864 2000 19.08207 2001 19.25919 2002 19.6236 2003 19.42637 2004 19.24654 2005 19.46849 2006 19.15184 2007 19.22836 2008 18.83262 2009 19.43459 2010 19.66626 2011 19.203 2012 19.27395 2013 19.17128 2014 19.28003 2015 19.58675 2016 19.59227 2017 19.53869 2018 19.52727