# year    value 
 1980 -10.30752 
 1981 -9.577468 
 1982 -11.8495 
 1983 -10.15639 
 1984 -10.6879 
 1985 -10.40451 
 1986 -10.02913 
 1987 -10.66177 
 1988 -9.78399 
 1989 -10.79894 
 1990 -11.03372 
 1991 -9.356954 
 1992 -11.58845 
 1993 -10.30032 
 1994 -10.02101 
 1995 -8.865109 
 1996 -10.68713 
 1997 -9.553421 
 1998 -10.61328 
 1999 -10.00045 
 2000 -10.17159 
 2001 -9.705818 
 2002 -8.711553 
 2003 -8.837563 
 2004 -9.527805 
 2005 -8.309635 
 2006 -9.124116 
 2007 -8.326541 
 2008 -9.008403 
 2009 -9.299572 
 2010 -8.569134 
 2011 -9.476379 
 2012 -9.159389 
 2013 -9.114359 
 2014 -8.829357 
 2015 -8.84137 
 2016 -8.720594 
 2017 -8.989917 
 2018 -7.865912