# year    value 
 1980 -8.991229 
 1981 -7.907459 
 1982 -10.1393 
 1983 -8.089084 
 1984 -9.320733 
 1985 -8.33457 
 1986 -8.831138 
 1987 -9.167687 
 1988 -8.272445 
 1989 -9.254129 
 1990 -9.791045 
 1991 -8.128105 
 1992 -10.12383 
 1993 -8.970881 
 1994 -8.589802 
 1995 -7.721024 
 1996 -8.496555 
 1997 -8.202471 
 1998 -9.183056 
 1999 -8.594009 
 2000 -8.754027 
 2001 -7.992374 
 2002 -7.648012 
 2003 -7.139388 
 2004 -7.808373 
 2005 -6.534114 
 2006 -7.265819 
 2007 -7.101701 
 2008 -7.193739 
 2009 -7.583776 
 2010 -6.431159 
 2011 -7.076989 
 2012 -7.001636 
 2013 -7.230948 
 2014 -7.719451 
 2015 -7.095716 
 2016 -6.393713 
 2017 -6.893065 
 2018 -6.814627