# year    value 
 1960 25.66212 
 1961 25.33717 
 1962 25.53305 
 1963  25.6714 
 1964 25.36711 
 1965 25.43235 
 1966 25.69111 
 1967 25.23726 
 1968 25.37182 
 1969 25.90445 
 1970 25.60888 
 1971 25.23722 
 1972 25.53747 
 1973 25.72332 
 1974 25.31859 
 1975 25.32045 
 1976 25.37486 
 1977 25.60068 
 1978    25.64 
 1979 25.88356 
 1980  25.8922 
 1981 25.72463 
 1982  25.6245 
 1983 25.78283 
 1984 25.69461 
 1985 25.73532 
 1986 25.70237 
 1987 26.17612 
 1988 25.90962 
 1989 25.59431 
 1990 26.02421 
 1991 25.85304 
 1992 25.56419 
 1993 25.85417 
 1994  25.7999 
 1995 25.96255 
 1996 25.98314 
 1997 26.00034 
 1998 26.43552 
 1999 26.05453 
 2000 25.97972 
 2001 26.21543 
 2002 26.32471 
 2003 26.34036 
 2004 26.31101 
 2005 26.36996 
 2006  26.2956 
 2007 26.27022 
 2008 26.11959 
 2009 26.52616 
 2010   26.744 
 2011  26.2342 
 2012 26.24635 
 2013  26.2621 
 2014 26.30065 
 2015 26.41679 
 2016 26.61067 
 2017 26.40714 
 2018 26.33485