# year    value 
 1980 8.547758 
 1981 8.454328 
 1982 8.178693 
 1983 8.050206 
 1984 7.624235 
 1985 8.936002 
 1986 8.602181 
 1987 8.837496 
 1988 8.455112 
 1989 8.394815 
 1990 8.670464 
 1991  8.55105 
 1992 8.171697 
 1993 8.704752 
 1994 8.787654 
 1995 8.104265 
 1996 8.482878 
 1997 8.732042 
 1998 9.154394 
 1999 8.743619 
 2000 8.358543 
 2001 8.786285 
 2002 8.486434 
 2003 8.754019 
 2004 8.914956 
 2005 8.890953 
 2006 8.889666 
 2007 7.906222 
 2008 8.683644 
 2009 9.050136 
 2010 8.325049 
 2011  8.60692 
 2012 8.534915 
 2013 9.066079 
 2014 9.216141 
 2015 9.106602 
 2016 8.890934 
 2017 9.258688 
 2018 8.480912