# year    value 
 1940 9.300638 
 1941 9.692989 
 1942 10.28793 
 1943 11.36014 
 1944 10.38135 
 1945 11.17736 
 1946 11.07941 
 1947 11.34277 
 1948 11.18369 
 1949 11.36342 
 1950  11.3812 
 1951 11.23541 
 1952 10.78894 
 1953 10.95641 
 1954 10.09982 
 1955 10.40196 
 1956 9.698161 
 1957 10.93247 
 1958 10.98475 
 1959   11.243 
 1960 10.85608 
 1961 11.52462 
 1962 10.03286 
 1963 10.01089 
 1964 10.63907 
 1965 10.03927 
 1966 11.05209 
 1967  10.9941 
 1968 10.62672 
 1969 10.32878 
 1970 10.40721 
 1971  10.6711 
 1972 10.52136 
 1973 10.55047 
 1974 11.01519 
 1975 11.00331 
 1976 10.67543 
 1977 10.98613 
 1978 10.07474 
 1979 10.76642 
 1980 10.00473 
 1981 10.73991 
 1982 11.28452 
 1983 11.28038 
 1984 10.39537 
 1985 10.31892 
 1986 10.66693 
 1987 10.53511 
 1988 11.33136 
 1989 11.47262 
 1990  11.6794 
 1991 10.74277 
 1992 11.66554 
 1993 11.13715 
 1994 12.31439 
 1995 11.29024 
 1996  10.4858 
 1997 11.50487 
 1998 11.51111 
 1999 11.61294 
 2000 12.29279 
 2001 11.54762 
 2002 12.12671 
 2003 11.82907 
 2004 11.35958 
 2005  11.0467 
 2006 11.79239 
 2007 12.20668 
 2008 11.95749 
 2009 11.99998 
 2010  10.9981 
 2011  12.2972 
 2012  12.0328 
 2013 11.65831 
 2014 12.76624 
 2015 12.59859 
 2016 12.15255 
 2017 12.17799 
 2018 12.93983