# year    value 
 1940 12.39121 
 1941 12.85421 
 1942 12.40583 
 1943 12.08917 
 1944 12.04222 
 1945 11.98549 
 1946 12.53891 
 1947 12.25629 
 1948 12.28269 
 1949 11.91679 
 1950 11.65168 
 1951 11.95844 
 1952 11.99143 
 1953 12.38236 
 1954 11.71437 
 1955 12.07496 
 1956 11.75591 
 1957 11.58543 
 1958 12.40478 
 1959 12.04229 
 1960  12.0496 
 1961 12.16692 
 1962 11.96855 
 1963 12.30861 
 1964 11.79419 
 1965 12.11518 
 1966 12.26935 
 1967 11.68687 
 1968 11.82084 
 1969 11.82305 
 1970 11.96074 
 1971 12.02577 
 1972 11.83562 
 1973 12.33664 
 1974 11.84428 
 1975 12.07098 
 1976  11.7904 
 1977 12.21234 
 1978 12.25339 
 1979  12.4154 
 1980 12.39153 
 1981 12.28995 
 1982 12.17954 
 1983 12.18532 
 1984 11.82645 
 1985 12.13387 
 1986 12.09807 
 1987 12.56057 
 1988  12.6219 
 1989 12.27107 
 1990 12.58797 
 1991 12.32177 
 1992  12.0754 
 1993 12.13304 
 1994 12.54537 
 1995 12.47582 
 1996 12.16589 
 1997  12.3977 
 1998 13.05322 
 1999 13.05263 
 2000 12.62036 
 2001 12.91912 
 2002 13.06312 
 2003 12.66069 
 2004 13.08536 
 2005 12.74381 
 2006 13.25176 
 2007  13.2236 
 2008 12.79026 
 2009 13.17144 
 2010 13.10182 
 2011 12.65711 
 2012 12.41755 
 2013 13.01844 
 2014 12.70788 
 2015 13.11925 
 2016 13.33122 
 2017 13.25944 
 2018 13.02677