# year    value 
 1980 26.30536 
 1981 26.47634 
 1982 26.23429 
 1983 26.50029 
 1984 26.35402 
 1985 26.24683 
 1986 26.21869 
 1987 26.43023 
 1988  26.6225 
 1989 26.16395 
 1990 26.36237 
 1991 26.58402 
 1992 26.10855 
 1993 26.02187 
 1994 26.57471 
 1995 26.79344 
 1996 26.24941 
 1997 26.70114 
 1998 26.95123 
 1999 26.66232 
 2000 26.85499 
 2001 26.66182 
 2002 26.96136 
 2003 26.48866 
 2004 26.60784 
 2005 27.13218 
 2006 26.92787 
 2007 27.09383 
 2008 26.83512 
 2009  26.9435 
 2010 27.23622 
 2011 27.03136 
 2012 27.05503 
 2013 26.79292 
 2014 26.94341 
 2015 26.90604 
 2016 27.23746 
 2017 27.20117 
 2018 27.25318