# year    value 
 1980 -9.724076 
 1981 -8.660534 
 1982 -10.42981 
 1983 -9.620382 
 1984 -9.944258 
 1985 -9.976953 
 1986 -9.865552 
 1987 -10.31979 
 1988 -9.146951 
 1989 -9.490275 
 1990 -9.536586 
 1991 -9.22379 
 1992 -10.02528 
 1993 -9.296142 
 1994 -9.658968 
 1995 -8.56276 
 1996 -9.375507 
 1997 -9.118554 
 1998 -9.364582 
 1999 -9.567954 
 2000 -9.088093 
 2001 -9.071424 
 2002 -8.92365 
 2003 -8.448406 
 2004 -9.491355 
 2005 -8.094555 
 2006 -8.790411 
 2007 -8.210637 
 2008 -8.688286 
 2009 -9.147046 
 2010 -8.448317 
 2011 -8.175687 
 2012 -8.657322 
 2013 -8.745675 
 2014 -8.35871 
 2015 -8.323686 
 2016 -7.594721 
 2017 -8.093968 
 2018 -8.525492