# year    value 
 1980 -9.47318 
 1981 -8.406001 
 1982 -10.13548 
 1983 -9.392008 
 1984 -9.669433 
 1985 -9.760004 
 1986 -9.701189 
 1987  -10.051 
 1988 -8.921512 
 1989 -9.254877 
 1990 -9.286614 
 1991 -9.006636 
 1992 -9.788458 
 1993 -9.068098 
 1994 -9.39524 
 1995 -8.314647 
 1996 -9.032304 
 1997 -8.93435 
 1998 -9.06886 
 1999 -9.197039 
 2000 -8.820072 
 2001 -8.777466 
 2002 -8.740242 
 2003 -8.196389 
 2004 -9.263504 
 2005 -7.797254 
 2006 -8.434976 
 2007 -7.951451 
 2008 -8.367248 
 2009 -8.877453 
 2010 -8.144529 
 2011 -7.830466 
 2012 -8.284271 
 2013 -8.476669 
 2014 -8.168446 
 2015 -8.11283 
 2016 -7.350443 
 2017 -7.869386 
 2018 -8.369155