# year    value 
 1980 24.59613 
 1981 24.31277 
 1982 24.04952 
 1983 24.67765 
 1984 24.19977 
 1985 24.32911 
 1986 24.59468 
 1987 24.62434 
 1988 24.60159 
 1989 24.14398 
 1990 24.59368 
 1991 24.52673 
 1992 24.79129 
 1993 24.64526 
 1994 24.41198 
 1995 24.33979 
 1996 24.33415 
 1997 24.17377 
 1998  25.0822 
 1999 24.37842 
 2000 24.16365 
 2001 24.42869 
 2002 25.00311 
 2003 24.71789 
 2004 24.65061 
 2005 25.11007 
 2006 24.26912 
 2007 24.73134 
 2008 24.18176 
 2009  24.5857 
 2010 24.91954 
 2011 24.20491 
 2012 24.32656 
 2013 24.71452 
 2014 24.78681 
 2015 24.67171 
 2016 25.14885 
 2017 24.82867 
 2018 24.88752