# year    value 
 1980 -11.89531 
 1981 -11.58758 
 1982 -12.46052 
 1983 -12.65767 
 1984 -12.04275 
 1985 -12.5769 
 1986 -12.16527 
 1987 -12.81678 
 1988 -11.43611 
 1989 -11.52909 
 1990 -9.750965 
 1991 -11.40793 
 1992 -12.10886 
 1993 -11.1963 
 1994 -11.40415 
 1995 -10.50576 
 1996 -11.17069 
 1997 -10.67221 
 1998 -11.20408 
 1999 -11.97042 
 2000 -10.65928 
 2001 -11.65405 
 2002 -11.27733 
 2003 -10.67218 
 2004 -11.96368 
 2005 -10.37866 
 2006 -11.15562 
 2007 -10.30106 
 2008 -11.13042 
 2009 -11.62265 
 2010 -9.863169 
 2011 -9.816577 
 2012 -10.67634 
 2013 -11.43005 
 2014 -10.02222 
 2015 -10.23503 
 2016 -9.28228 
 2017 -10.20478 
 2018 -11.51088