# year    value 
 1980 7.439127 
 1981 7.818851 
 1982 7.157169 
 1983 7.468653 
 1984   7.7389 
 1985 7.420447 
 1986  7.01284 
 1987 7.121982 
 1988 8.048256 
 1989 7.865315 
 1990 8.161283 
 1991 8.260771 
 1992 6.829034 
 1993 7.785946 
 1994 7.955132 
 1995 8.019575 
 1996 7.447217 
 1997 7.766425 
 1998 8.565945 
 1999 7.625525 
 2000 8.027372 
 2001 8.394425 
 2002 8.279985 
 2003 8.484739 
 2004 7.834902 
 2005 8.334642 
 2006 8.348649 
 2007 8.502182 
 2008 8.151538 
 2009 8.061087 
 2010 8.393384 
 2011 8.511142 
 2012  8.61093 
 2013 8.638767 
 2014 8.425087 
 2015 8.151815 
 2016 9.069977 
 2017 8.341328 
 2018 8.216637