# year    value 
 1980 -9.25426 
 1981 -8.324661 
 1982 -9.961313 
 1983 -9.174733 
 1984 -9.434219 
 1985 -9.439251 
 1986 -9.475413 
 1987 -9.860626 
 1988 -8.765317 
 1989 -9.075927 
 1990 -9.222849 
 1991 -8.882505 
 1992 -9.778433 
 1993 -8.971613 
 1994 -9.256558 
 1995 -8.10522 
 1996 -8.84148 
 1997 -8.808472 
 1998 -9.060225 
 1999 -9.289601 
 2000 -8.749753 
 2001 -8.688354 
 2002 -8.575286 
 2003 -7.995433 
 2004 -9.101502 
 2005 -7.61565 
 2006 -8.207929 
 2007 -7.776074 
 2008 -8.15877 
 2009 -8.643308 
 2010 -7.658283 
 2011 -7.691704 
 2012 -7.84724 
 2013 -8.271295 
 2014 -7.976904 
 2015 -7.882178 
 2016 -6.826556 
 2017 -7.32798 
 2018 -7.790517