# year    value 
 1980 27.22942 
 1981 26.96493 
 1982 26.61808 
 1983 26.90327 
 1984 27.14163 
 1985 26.91809 
 1986 26.91447 
 1987 26.99568 
 1988 27.36547 
 1989 26.68883 
 1990 26.95233 
 1991 27.05576 
 1992 26.73382 
 1993 26.83613 
 1994 27.09891 
 1995 27.00806 
 1996  27.0491 
 1997 26.74529 
 1998 27.60032 
 1999 27.24165 
 2000 27.26149 
 2001 27.53921 
 2002 27.60995 
 2003 27.52179 
 2004 27.51298 
 2005 27.59859 
 2006  27.3511 
 2007 27.56115 
 2008 27.46767 
 2009 27.49577 
 2010 28.13075 
 2011 27.42112 
 2012 27.37896 
 2013 27.60174 
 2014 27.48058 
 2015 27.46672 
 2016 27.98339 
 2017 27.59388 
 2018 27.57356