# year    value 
 1980 26.49651 
 1981 26.28798 
 1982 26.45513 
 1983 26.92272 
 1984  26.2751 
 1985 26.44633 
 1986 26.43982 
 1987 26.55224 
 1988 26.80045 
 1989 26.21851 
 1990  26.4331 
 1991 26.61273 
 1992 26.58288 
 1993 26.29125 
 1994 26.46858 
 1995 26.66236 
 1996 26.48891 
 1997 26.41861 
 1998 27.16506 
 1999 26.57121 
 2000 26.24139 
 2001 26.46054 
 2002 26.44065 
 2003 26.95838 
 2004 26.82627 
 2005 26.98779 
 2006 26.78477 
 2007 26.76788 
 2008 26.42932 
 2009 26.59652 
 2010 26.99369 
 2011 26.42605 
 2012 26.42794 
 2013 26.93982 
 2014 26.70016 
 2015 26.83075 
 2016  27.2827 
 2017 26.90641 
 2018 26.80783