# year    value 
 1980 -25.10232 
 1981 -23.81857 
 1982 -25.8169 
 1983 -25.47306 
 1984 -25.22376 
 1985 -26.70772 
 1986 -24.70019 
 1987 -26.36341 
 1988 -25.36842 
 1989 -24.65878 
 1990 -26.49529 
 1991 -25.92097 
 1992 -25.11123 
 1993 -24.24884 
 1994 -26.78429 
 1995 -23.92265 
 1996 -25.10358 
 1997 -25.53809 
 1998 -26.02165 
 1999 -25.47756 
 2000 -24.53607 
 2001 -25.63874 
 2002 -24.95743 
 2003 -24.59324 
 2004 -24.63335 
 2005 -24.97251 
 2006 -24.4919 
 2007 -23.51896 
 2008 -24.06303 
 2009 -25.19784 
 2010 -25.14471 
 2011 -24.77108 
 2012 -23.71033 
 2013 -25.62299 
 2014 -24.00424 
 2015 -23.41381 
 2016 -22.46437 
 2017 -23.84278 
 2018 -23.28461