# year    value 
 1979 -28.55361 
 1980 -25.31154 
 1981 -24.0912 
 1982 -26.59795 
 1983 -25.45446 
 1984 -25.59525 
 1985 -25.98547 
 1986 -24.01746 
 1987 -25.95296 
 1988 -26.00581 
 1989 -24.81908 
 1990 -26.81923 
 1991 -26.00255 
 1992 -25.09524 
 1993 -24.86774 
 1994 -26.39523 
 1995 -24.70939 
 1996 -25.69314 
 1997 -25.07677 
 1998 -26.05689 
 1999 -26.80655 
 2000 -25.26166 
 2001 -25.46763 
 2002 -25.84356 
 2003 -24.50147 
 2004 -25.19356 
 2005 -25.91629 
 2006 -25.39225 
 2007 -24.83982 
 2008 -25.31608 
 2009 -26.44045 
 2010 -25.38309 
 2011 -25.68539 
 2012 -24.87807 
 2013 -26.44389 
 2014 -24.06376 
 2015 -23.61932 
 2016 -23.4292 
 2017 -24.05025 
 2018 -23.22934