# year    value 
 1980 -8.764575 
 1981 -7.53868 
 1982 -9.835732 
 1983 -7.710896 
 1984 -9.032942 
 1985 -7.957507 
 1986 -8.651398 
 1987 -8.883319 
 1988 -8.037041 
 1989 -8.963146 
 1990 -9.488725 
 1991 -7.911439 
 1992 -9.776847 
 1993 -8.64097 
 1994 -8.221992 
 1995 -7.528332 
 1996 -7.961334 
 1997 -7.804531 
 1998 -8.739919 
 1999 -8.256717 
 2000 -8.300832 
 2001 -7.539482 
 2002 -7.36848 
 2003 -6.762209 
 2004 -7.465522 
 2005 -6.236738 
 2006 -7.092336 
 2007 -6.861292 
 2008 -6.867286 
 2009 -7.28597 
 2010 -5.983512 
 2011 -6.518554 
 2012 -6.612945 
 2013 -6.893106 
 2014 -7.526123 
 2015 -6.792469 
 2016 -5.981251 
 2017 -6.514993 
 2018 -6.711288