# year    value 
 1979 24.65452 
 1980 24.67524 
 1981 24.43166 
 1982 24.33873 
 1983 24.58596 
 1984 24.32003 
 1985 24.39479 
 1986 24.39442 
 1987 25.03116 
 1988 24.56202 
 1989 24.76673 
 1990 25.05817 
 1991 24.54225 
 1992 24.31197 
 1993 24.91411 
 1994 24.66648 
 1995 24.82937 
 1996 24.61911 
 1997 25.05301 
 1998 25.20948 
 1999 24.87932 
 2000 24.70664 
 2001 25.07077 
 2002  25.0971 
 2003  25.2345 
 2004 25.04668 
 2005 25.21349 
 2006 25.16351 
 2007 25.04538 
 2008  25.0858 
 2009 25.40882 
 2010 25.45297 
 2011 25.02966 
 2012 25.33669 
 2013 25.14827 
 2014 25.31279 
 2015 25.81332 
 2016 25.65642 
 2017 25.46031 
 2018 25.51549