# year    value 
 1980 25.77453 
 1981 25.51304 
 1982 25.42189 
 1983 25.66348 
 1984 25.43373 
 1985 25.49928 
 1986 25.51042 
 1987 26.13404 
 1988 25.63767 
 1989 25.87926 
 1990 26.18073 
 1991 25.65134 
 1992 25.42734 
 1993 26.03974 
 1994  25.7377 
 1995 25.89992 
 1996 25.67544 
 1997 26.20964 
 1998 26.25204 
 1999 25.96447 
 2000 25.81083 
 2001 26.17158 
 2002   26.221 
 2003 26.34269 
 2004 26.19272 
 2005 26.28746 
 2006 26.24993 
 2007 26.16095 
 2008 26.18787 
 2009 26.49509 
 2010 26.58585 
 2011 26.10547 
 2012 26.45461 
 2013 26.25965 
 2014  26.4143 
 2015 26.90346 
 2016  26.7257 
 2017 26.50373 
 2018 26.66488