# year    value 
 1980 28.61529 
 1981 28.65714 
 1982 28.73293 
 1983 29.02702 
 1984 28.61529 
 1985 28.55843 
 1986 28.71488 
 1987 29.30109 
 1988 28.75582 
 1989 28.71366 
 1990 28.86337 
 1991 28.71926 
 1992 28.67915 
 1993 28.91366 
 1994 28.59741 
 1995  29.1267 
 1996 28.81977 
 1997 29.05078 
 1998 29.34245 
 1999 28.78481 
 2000 28.88287 
 2001 28.91423 
 2002 29.25398 
 2003 29.08787 
 2004 29.03463 
 2005 29.17489 
 2006 29.23009 
 2007 29.03555 
 2008 29.01817 
 2009 29.47766 
 2010 29.32481 
 2011 29.29181 
 2012  29.1275 
 2013 28.98401 
 2014 29.31117 
 2015 29.45441 
 2016 29.32144 
 2017 29.30251 
 2018 29.14193