# year    value 
 1980 -11.99622 
 1981 -11.38393 
 1982 -12.52288 
 1983 -12.53204 
 1984 -11.9575 
 1985 -12.71763 
 1986 -12.28551 
 1987 -12.87461 
 1988 -11.40953 
 1989 -11.50894 
 1990 -9.563576 
 1991 -11.38718 
 1992 -12.07425 
 1993 -11.14481 
 1994 -11.46199 
 1995 -10.62481 
 1996 -11.18949 
 1997 -10.68071 
 1998 -11.30787 
 1999 -12.09719 
 2000 -10.69097 
 2001 -11.64031 
 2002 -11.17891 
 2003 -10.6863 
 2004 -11.84971 
 2005 -10.29527 
 2006 -11.38397 
 2007 -10.3506 
 2008 -11.03091 
 2009 -11.54235 
 2010 -9.993237 
 2011 -9.815416 
 2012 -10.80483 
 2013 -11.39751 
 2014 -9.976148 
 2015 -10.26206 
 2016 -9.256727 
 2017 -10.08762 
 2018 -11.35814