# year value 1901 15.28475 1902 15.20149 1903 15.03078 1904 14.97793 1905 14.76544 1906 15.05759 1907 15.40608 1908 15.0613 1909 15.15168 1910 14.98867 1911 15.1327 1912 15.10161 1913 14.94487 1914 15.24003 1915 15.3005 1916 15.41935 1917 15.05444 1918 14.85589 1919 15.23231 1920 15.03972 1921 15.24737 1922 15.67592 1923 15.36398 1924 15.45214 1925 14.698 1926 15.38083 1927 15.36901 1928 15.6587 1929 15.37149 1930 15.0207 1931 15.50276 1932 15.38032 1933 15.23943 1934 15.30571 1935 15.48503 1936 15.26484 1937 15.4842 1938 15.58568 1939 15.50462 1940 15.44985 1941 16.0323 1942 15.77543 1943 15.26228 1944 15.55046 1945 14.89618 1946 15.65278 1947 15.67681 1948 15.56968 1949 15.33557 1950 15.24929 1951 15.13382 1952 15.83528 1953 15.6346 1954 15.75814 1955 15.21346 1956 15.14151 1957 15.05827 1958 15.51302 1959 15.43831 1960 15.59477 1961 15.28184 1962 15.05046 1963 15.25871 1964 14.95254 1965 15.05873 1966 15.66519 1967 15.09781 1968 14.54247 1969 15.62307 1970 15.49425 1971 15.19945 1972 15.00135 1973 15.78509 1974 14.91585 1975 15.22562 1976 14.98684 1977 15.13537 1978 15.46745 1979 15.809 1980 15.61076 1981 15.54451 1982 15.42679 1983 14.85367 1984 14.93143 1985 15.39389 1986 15.41016 1987 15.74934 1988 15.80877 1989 15.16912 1990 15.51133 1991 15.93022 1992 14.94336 1993 15.50768 1994 15.81638 1995 15.63553 1996 15.69973 1997 15.44563 1998 16.08585 1999 16.33873 2000 15.53603 2001 15.92044 2002 16.12739 2003 16.26878 2004 15.94561 2005 15.99799 2006 16.33755 2007 15.84089 2008 15.56472 2009 16.39988 2010 16.42811 2011 15.80837 2012 15.66572 2013 16.31181 2014 15.62318 2015 15.97139 2016 16.15551 2017 16.57824 2018 16.13469