# year    value 
 1980 -6.608949 
 1981 -5.888371 
 1982 -6.859475 
 1983 -5.624957 
 1984 -6.947229 
 1985 -8.059731 
 1986 -6.631189 
 1987 -6.091691 
 1988 -6.361084 
 1989 -5.983082 
 1990 -5.800512 
 1991 -6.266055 
 1992 -5.746605 
 1993 -6.357872 
 1994 -6.812675 
 1995 -5.407009 
 1996 -6.972632 
 1997  -6.0777 
 1998 -5.555779 
 1999 -4.939653 
 2000 -5.405394 
 2001 -6.450172 
 2002 -4.753248 
 2003 -6.619384 
 2004 -5.317291 
 2005 -6.656979 
 2006 -6.196846 
 2007 -4.733739 
 2008 -6.675181 
 2009 -6.120774 
 2010 -6.814981 
 2011 -6.802355 
 2012 -6.66043 
 2013 -6.433641 
 2014 -6.369903 
 2015 -5.175203 
 2016 -4.442289 
 2017 -5.274038 
 2018 -5.963971