# year    value 
 1979 -9.905365 
 1980 -9.831936 
 1981 -9.275342 
 1982 -11.26531 
 1983 -9.491868 
 1984 -10.38822 
 1985 -9.733181 
 1986 -9.497833 
 1987 -10.22248 
 1988 -9.14561 
 1989 -10.33346 
 1990 -10.91242 
 1991 -8.931766 
 1992 -11.41085 
 1993 -10.1946 
 1994 -9.954094 
 1995 -8.435758 
 1996 -10.48181 
 1997 -9.678517 
 1998 -10.82675 
 1999 -9.845106 
 2000 -10.43503 
 2001 -9.672252 
 2002 -8.684862 
 2003 -8.53843 
 2004 -9.080087 
 2005 -7.63715 
 2006 -7.909303 
 2007 -7.993433 
 2008 -8.404628 
 2009 -8.688408 
 2010 -8.091586 
 2011 -9.148351 
 2012 -8.443377 
 2013 -8.484083 
 2014 -8.436548 
 2015 -8.220531 
 2016 -7.923626 
 2017 -8.29542 
 2018 -7.197933