# year    value 
 1980 8.549762 
 1981 8.818406 
 1982 8.319162 
 1983 8.879519 
 1984 8.305871 
 1985 7.791785 
 1986 8.464876 
 1987 8.503933 
 1988 8.734526 
 1989 8.563802 
 1990 8.628619 
 1991 8.694759 
 1992  8.65613 
 1993 8.637496 
 1994 8.144565 
 1995 9.100337 
 1996   8.4493 
 1997 8.622538 
 1998 9.084003 
 1999 9.238876 
 2000 9.047227 
 2001 8.581928 
 2002  9.30528 
 2003 8.826143 
 2004 9.263003 
 2005 8.891158 
 2006  9.09683 
 2007 9.557372 
 2008 8.710718 
 2009 8.956661 
 2010 8.901833 
 2011 8.667655 
 2012 8.861648 
 2013 8.898762 
 2014 8.853686 
 2015 9.327842 
 2016 10.03527 
 2017 9.467077 
 2018 9.233799