# year value 1901 15.25952 1902 14.93755 1903 15.04476 1904 15.20781 1905 15.37129 1906 15.17276 1907 15.06108 1908 15.07244 1909 15.4089 1910 14.98438 1911 15.21583 1912 14.86857 1913 15.27532 1914 15.223 1915 15.26177 1916 15.10159 1917 15.09107 1918 15.31642 1919 15.15026 1920 15.11612 1921 15.16929 1922 15.20972 1923 15.57005 1924 15.39605 1925 15.30127 1926 15.47372 1927 15.58129 1928 15.50648 1929 15.4011 1930 15.45174 1931 15.61787 1932 15.43726 1933 15.23283 1934 15.50462 1935 15.26976 1936 15.46342 1937 15.70226 1938 15.87086 1939 15.31107 1940 15.50915 1941 15.33542 1942 15.54942 1943 15.60361 1944 15.68466 1945 15.40222 1946 15.37197 1947 15.67146 1948 15.60939 1949 15.40222 1950 15.02782 1951 15.46161 1952 15.10138 1953 15.38901 1954 15.58833 1955 15.30908 1956 14.85312 1957 15.43274 1958 15.33849 1959 15.15445 1960 15.28867 1961 15.35545 1962 15.53912 1963 15.83973 1964 15.0421 1965 15.22271 1966 15.24784 1967 15.55493 1968 15.1791 1969 15.46614 1970 15.33356 1971 15.43007 1972 15.1272 1973 15.33999 1974 14.97884 1975 15.23464 1976 14.81146 1977 15.51463 1978 15.31224 1979 15.55405 1980 15.57573 1981 15.58765 1982 15.31386 1983 15.85351 1984 15.25527 1985 15.37366 1986 15.27001 1987 15.57315 1988 15.6673 1989 15.5137 1990 15.78519 1991 15.72639 1992 15.09483 1993 15.22411 1994 15.9157 1995 15.94068 1996 15.52288 1997 15.97653 1998 15.90481 1999 15.88766 2000 15.59235 2001 16.06895 2002 16.02638 2003 16.1677 2004 16.23309 2005 16.53404 2006 16.17313 2007 16.25736 2008 16.27468 2009 16.27868 2010 16.42897 2011 16.17194 2012 16.32482 2013 16.29597 2014 16.11386 2015 16.50795 2016 16.27103 2017 16.31446 2018 16.17954