# year    value 
 1979 25.33102 
 1980 25.71723 
 1981 25.41138 
 1982  25.0324 
 1983 25.34258 
 1984 25.57349 
 1985 25.24312 
 1986 25.32488 
 1987 25.52887 
 1988 25.85774 
 1989 25.13723 
 1990 25.41364 
 1991 25.57682 
 1992 25.17354 
 1993 25.30535 
 1994 25.60166 
 1995 25.54559 
 1996 25.50089 
 1997 25.07985 
 1998 26.16667 
 1999  25.7263 
 2000 25.68037 
 2001 25.85315 
 2002 25.94503 
 2003 25.93172 
 2004 25.90465 
 2005  26.0297 
 2006  25.8896 
 2007 25.98483 
 2008 25.87344 
 2009  25.9238 
 2010 26.67808 
 2011 25.84209 
 2012 25.87424 
 2013 26.23199 
 2014 26.05256 
 2015 26.05412 
 2016 26.73037 
 2017 26.36003 
 2018 26.28265