# year    value 
 1980 -12.34442 
 1981 -10.68114 
 1982 -12.73808 
 1983 -12.0985 
 1984 -11.66333 
 1985 -13.20325 
 1986 -12.70043 
 1987 -13.07416 
 1988 -11.31782 
 1989 -11.43938 
 1990 -8.916918 
 1991 -11.3156 
 1992 -11.9548 
 1993 -10.96714 
 1994 -11.66159 
 1995 -11.03562 
 1996 -11.25436 
 1997 -10.71002 
 1998 -11.66604 
 1999 -12.53466 
 2000 -10.80032 
 2001 -11.59288 
 2002 -10.83928 
 2003 -10.73504 
 2004 -11.45644 
 2005 -10.0075 
 2006 -12.17195 
 2007 -10.52155 
 2008 -10.68751 
 2009 -11.26522 
 2010 -10.44209 
 2011 -9.811411 
 2012 -11.24822 
 2013 -11.28523 
 2014 -9.817158 
 2015 -10.35537 
 2016 -9.168548 
 2017 -9.683318 
 2018 -10.83105