# year    value 
 1979 -9.677336 
 1980 -9.006874 
 1981 -8.607063 
 1982 -9.12141 
 1983 -9.132115 
 1984 -9.666449 
 1985 -10.44991 
 1986 -9.113103 
 1987 -8.593005 
 1988 -8.807833 
 1989 -8.940447 
 1990 -8.546716 
 1991 -8.760572 
 1992 -8.69488 
 1993 -9.007163 
 1994 -8.664291 
 1995 -8.196712 
 1996 -9.098312 
 1997 -8.528345 
 1998 -8.602214 
 1999 -7.650846 
 2000 -8.718655 
 2001 -9.175753 
 2002 -7.792968 
 2003 -8.408092 
 2004 -8.040433 
 2005 -9.131963 
 2006 -8.49917 
 2007 -7.594315 
 2008 -9.200335 
 2009 -8.349933 
 2010 -8.765452 
 2011 -8.991242 
 2012 -9.370277 
 2013 -9.144722 
 2014 -8.425455 
 2015 -7.182907 
 2016 -7.569088 
 2017 -7.656803 
 2018 -8.030516 
 2019 -8.537432