# year    value 
 1980 26.83136 
 1981 26.56611 
 1982 26.13163 
 1983 26.49473 
 1984 26.68075 
 1985 26.35048 
 1986 26.46111 
 1987 26.68668 
 1988 26.99026 
 1989 26.24693 
 1990 26.56729 
 1991 26.67324 
 1992 26.27618 
 1993 26.44763 
 1994 26.69575 
 1995 26.63712 
 1996 26.64599 
 1997 26.20228 
 1998 27.26048 
 1999 26.78627 
 2000  26.7794 
 2001 26.97856 
 2002 27.04174 
 2003  27.0349 
 2004 27.00105 
 2005 27.18756 
 2006 26.99193 
 2007 27.09669 
 2008 26.97034 
 2009 27.00143 
 2010 27.84271 
 2011 26.96853 
 2012 26.96688 
 2013 27.35349 
 2014 27.16238 
 2015  27.1566 
 2016 27.86199 
 2017 27.49746 
 2018 27.38991