# year    value 
 1980 25.94402 
 1981 25.63804 
 1982 25.34718 
 1983 25.59113 
 1984 25.84309 
 1985 25.60713 
 1986 25.60518 
 1987  25.6757 
 1988 26.01981 
 1989  25.4008 
 1990 25.62695 
 1991 25.80335 
 1992 25.47027 
 1993 25.52884 
 1994 25.81606 
 1995 25.74901 
 1996 25.73203 
 1997 25.45888 
 1998 26.32746 
 1999 25.96752 
 2000 25.95858 
 2001 26.20313 
 2002 26.32324 
 2003 26.23806 
 2004 26.22907 
 2005 26.27397 
 2006 26.06946 
 2007 26.24609 
 2008 26.15745 
 2009 26.20871 
 2010 26.79331 
 2011 26.10591 
 2012 26.11468 
 2013  26.3137 
 2014 26.18842 
 2015 26.19802 
 2016  26.6893 
 2017 26.27908 
 2018 26.29853