# year    value 
 1980 25.45664 
 1981 25.27858 
 1982 25.42209 
 1983 25.89892 
 1984 25.27945 
 1985 25.38446 
 1986 25.40158 
 1987 25.56322 
 1988 25.78475 
 1989 25.21608 
 1990 25.41362 
 1991 25.57089 
 1992 25.55029 
 1993 25.28675 
 1994 25.46335 
 1995 25.66836 
 1996 25.46212 
 1997 25.40384 
 1998  26.1403 
 1999 25.55401 
 2000 25.25414 
 2001 25.46598 
 2002 25.42251 
 2003 25.93294 
 2004 25.79997 
 2005 25.95595 
 2006  25.7484 
 2007 25.74495 
 2008  25.3976 
 2009 25.58195 
 2010 25.99295 
 2011 25.42224 
 2012 25.42321 
 2013  25.9038 
 2014 25.69052 
 2015 25.79218 
 2016 26.28498 
 2017 25.92171 
 2018  25.7596