# year    value 
 1979 -7.443725 
 1980 -6.037296 
 1981 -5.383606 
 1982 -6.308873 
 1983 -5.155646 
 1984 -6.436537 
 1985 -7.605763 
 1986 -6.147106 
 1987 -5.573125 
 1988 -5.832851 
 1989 -5.435462 
 1990 -5.293713 
 1991 -5.723968 
 1992 -5.25364 
 1993 -5.763663 
 1994 -6.285244 
 1995 -4.797513 
 1996 -6.45139 
 1997 -5.50461 
 1998 -5.105867 
 1999 -4.396429 
 2000 -4.865045 
 2001 -5.931348 
 2002 -4.194141 
 2003 -5.993114 
 2004 -4.741549 
 2005 -5.932046 
 2006 -5.605671 
 2007 -4.040799 
 2008 -5.917549 
 2009 -5.44107 
 2010 -6.043713 
 2011 -6.077345 
 2012 -5.947654 
 2013 -5.831846 
 2014 -5.724309 
 2015 -4.570333 
 2016 -3.783972 
 2017 -4.523307 
 2018 -5.26901