# year    value 
 1980 -8.675076 
 1981 -8.258942 
 1982 -8.661836 
 1983 -8.65074 
 1984 -9.282032 
 1985 -9.947277 
 1986 -8.618103 
 1987 -8.225763 
 1988 -8.454613 
 1989 -8.506812 
 1990 -8.113792 
 1991 -8.413166 
 1992 -8.239788 
 1993 -8.688842 
 1994 -8.333364 
 1995 -7.859951 
 1996 -8.519842 
 1997 -8.116488 
 1998 -8.019544 
 1999 -7.275635 
 2000 -8.276635 
 2001 -8.707239 
 2002 -7.469077 
 2003 -8.212566 
 2004 -7.632097 
 2005 -9.054925 
 2006 -8.296117 
 2007 -7.352996 
 2008  -9.0444 
 2009 -8.050444 
 2010 -8.588717 
 2011 -8.751688 
 2012 -9.319829 
 2013 -8.828709 
 2014 -8.188306 
 2015 -7.075165 
 2016 -7.397095 
 2017 -7.646793 
 2018 -7.998235