# year    value 
 1980 -8.81231 
 1981 -7.616267 
 1982 -9.85472 
 1983 -7.947866 
 1984 -9.328282 
 1985 -8.267616 
 1986 -8.761891 
 1987 -9.04108 
 1988 -8.264339 
 1989 -9.039445 
 1990 -9.588303 
 1991 -7.865767 
 1992  -9.9037 
 1993 -8.913502 
 1994  -8.2084 
 1995 -7.690615 
 1996 -8.190745 
 1997 -7.822884 
 1998 -8.742164 
 1999 -8.051692 
 2000 -8.290534 
 2001 -7.64586 
 2002 -7.750182 
 2003 -7.211039 
 2004 -7.770074 
 2005 -6.384283 
 2006 -7.673751 
 2007 -7.046104 
 2008 -7.104589 
 2009 -7.407794 
 2010 -6.707886 
 2011 -6.998038 
 2012  -7.2812 
 2013 -7.254947 
 2014 -7.856495 
 2015 -7.416993 
 2016 -7.053965 
 2017 -7.359811 
 2018 -7.15012