# year value 1901 15.10309 1902 15.52955 1903 14.81939 1904 15.21758 1905 14.97242 1906 15.33608 1907 14.59034 1908 14.66575 1909 14.61566 1910 14.85577 1911 14.63204 1912 15.12416 1913 15.10388 1914 15.16224 1915 14.78396 1916 15.2525 1917 14.47676 1918 15.02346 1919 15.65569 1920 15.18079 1921 15.48851 1922 15.17857 1923 15.39793 1924 14.38572 1925 15.01113 1926 14.88251 1927 14.94274 1928 15.05228 1929 14.90456 1930 15.45404 1931 14.39536 1932 15.11707 1933 15.19989 1934 15.13415 1935 15.26438 1936 14.94863 1937 14.97012 1938 15.3789 1939 14.9993 1940 14.93497 1941 14.4968 1942 14.82301 1943 15.01664 1944 14.78142 1945 15.4425 1946 14.7365 1947 15.09854 1948 14.5965 1949 14.83593 1950 15.46448 1951 15.09444 1952 15.20631 1953 15.56791 1954 14.98979 1955 14.70316 1956 14.40952 1957 15.49336 1958 15.4083 1959 14.80508 1960 14.84566 1961 15.24473 1962 15.29613 1963 15.21655 1964 14.92108 1965 14.85121 1966 15.35073 1967 15.62851 1968 14.98621 1969 15.26312 1970 15.37402 1971 15.03902 1972 15.30061 1973 15.40409 1974 15.60631 1975 15.30094 1976 14.80757 1977 15.06141 1978 15.65279 1979 15.17541 1980 16.11231 1981 15.83092 1982 15.77574 1983 15.38938 1984 14.85204 1985 15.50913 1986 15.47669 1987 15.2445 1988 15.4438 1989 15.66778 1990 15.44706 1991 15.90625 1992 15.49964 1993 15.65827 1994 15.76422 1995 15.07588 1996 15.56341 1997 15.59866 1998 15.66796 1999 15.38601 2000 15.27903 2001 15.27756 2002 15.67817 2003 15.69184 2004 15.47795 2005 15.70319 2006 15.04862 2007 15.63701 2008 15.58562 2009 16.08337 2010 15.88528 2011 15.52485 2012 15.6278 2013 15.91682 2014 15.72479 2015 15.99291 2016 15.84252 2017 15.99507 2018 16.41313