# year    value 
 1979 -12.46509 
 1980 -11.4421 
 1981 -11.23033 
 1982 -12.0466 
 1983 -12.29339 
 1984 -11.76102 
 1985 -12.02187 
 1986 -11.71147 
 1987 -12.3119 
 1988 -11.14124 
 1989 -11.1749 
 1990 -9.523702 
 1991 -11.22291 
 1992 -11.96001 
 1993 -11.06355 
 1994 -10.9254 
 1995  -9.8883 
 1996 -10.47065 
 1997 -10.13158 
 1998 -10.58031 
 1999 -11.53504 
 2000 -10.11228 
 2001 -11.28546 
 2002 -10.74583 
 2003 -10.04877 
 2004 -11.63138 
 2005 -9.790277 
 2006 -10.61571 
 2007 -9.878073 
 2008 -10.49144 
 2009 -11.16117 
 2010 -9.038841 
 2011 -9.490178 
 2012 -10.09804 
 2013 -10.97061 
 2014 -9.388819 
 2015 -9.586761 
 2016 -8.701639 
 2017 -9.435463 
 2018 -10.96453