# year    value 
 1980 26.16531 
 1981  25.8988 
 1982 25.90331 
 1983 26.07447 
 1984 25.89611 
 1985  25.9562 
 1986 25.91906 
 1987 26.45429 
 1988 25.91493 
 1989 26.16078 
 1990 26.45045 
 1991 25.98871 
 1992 25.82291 
 1993 26.33778 
 1994 26.00867 
 1995 26.24801 
 1996 26.05568 
 1997 26.57155 
 1998  26.5698 
 1999 26.25455 
 2000 26.17099 
 2001 26.44254 
 2002  26.5461 
 2003 26.64142 
 2004 26.54679 
 2005 26.51494 
 2006 26.45163 
 2007 26.47598 
 2008 26.42754 
 2009 26.67433 
 2010 26.84027 
 2011 26.37886 
 2012 26.61373 
 2013 26.40948 
 2014 26.53142 
 2015 26.94234 
 2016  26.7787 
 2017 26.62688 
 2018 26.55453