# year    value 
 1979 -27.83894 
 1980 -23.6398 
 1981 -22.83095 
 1982 -24.60799 
 1983 -24.43115 
 1984 -24.07402 
 1985 -25.44135 
 1986 -23.62946 
 1987 -25.40408 
 1988 -24.39291 
 1989 -23.63774 
 1990 -25.48965 
 1991 -24.80541 
 1992 -24.15412 
 1993 -23.32304 
 1994 -25.83639 
 1995 -22.86968 
 1996 -23.74067 
 1997 -24.36001 
 1998 -25.18192 
 1999 -24.58957 
 2000 -23.41268 
 2001 -24.62517 
 2002 -23.99181 
 2003 -23.53692 
 2004 -23.6776 
 2005 -23.79695 
 2006 -23.40306 
 2007 -22.40913 
 2008 -22.92767 
 2009 -23.71825 
 2010 -23.72683 
 2011 -23.41626 
 2012 -22.40323 
 2013 -24.35375 
 2014 -23.26965 
 2015 -22.84903 
 2016 -21.56234 
 2017 -22.51949 
 2018 -21.52952