# year    value 
 1980 -5.559919 
 1981 -4.684765 
 1982 -5.944366 
 1983 -4.088682 
 1984 -5.761785 
 1985 -7.101372 
 1986 -5.622377 
 1987 -5.008162 
 1988 -5.298141 
 1989 -4.701714 
 1990 -4.625995 
 1991 -5.175906 
 1992 -4.480747 
 1993 -5.174373 
 1994 -6.04058 
 1995 -4.161582 
 1996 -6.187071 
 1997 -5.042551 
 1998 -4.304857 
 1999 -3.75361 
 2000 -3.947585 
 2001 -5.304197 
 2002 -3.374345 
 2003 -5.810481 
 2004 -4.141999 
 2005 -5.439475 
 2006 -5.130988 
 2007 -3.403869 
 2008 -5.472262 
 2009 -5.141027 
 2010 -5.914406 
 2011 -5.812624 
 2012 -5.310179 
 2013 -5.217599 
 2014 -5.446648 
 2015 -4.21054 
 2016 -2.942053 
 2017 -4.069324 
 2018 -4.931119