# year    value 
 1980 -24.31436 
 1981 -23.06163 
 1982 -24.87658 
 1983 -24.72042 
 1984 -24.35724 
 1985 -26.19021 
 1986 -24.23169 
 1987 -25.82629 
 1988 -24.52315 
 1989 -23.91284 
 1990 -25.66253 
 1991 -25.17658 
 1992 -24.42084 
 1993 -23.37148 
 1994 -26.12632 
 1995 -22.97221 
 1996 -24.36084 
 1997 -24.87944 
 1998 -25.35913 
 1999 -24.46399 
 2000 -23.65565 
 2001 -25.03773 
 2002 -24.00346 
 2003 -23.96098 
 2004 -23.77797 
 2005 -24.0367 
 2006 -23.58292 
 2007 -22.58079 
 2008 -23.09296 
 2009 -24.14663 
 2010 -24.43195 
 2011 -23.88597 
 2012 -22.67665 
 2013 -24.76147 
 2014 -23.3499 
 2015 -22.79251 
 2016 -21.67108 
 2017 -23.11677 
 2018 -22.5766