# year    value 
 1980 8.490002 
 1981 8.817427 
 1982 8.125763 
 1983 7.746233 
 1984 8.605283 
 1985 8.376335 
 1986 7.994705 
 1987 8.370489 
 1988 8.291716 
 1989 8.145194 
 1990 8.085052 
 1991 8.235326 
 1992 8.180412 
 1993  8.10266 
 1994 8.566599 
 1995 8.437458 
 1996 8.130445 
 1997 8.627814 
 1998 8.991094 
 1999 9.102165 
 2000  9.04108 
 2001 9.045539 
 2002 9.157207 
 2003 8.476205 
 2004 9.668484 
 2005 8.935918 
 2006 9.191607 
 2007 9.518121 
 2008 9.750817 
 2009 9.350543 
 2010 9.285879 
 2011  8.78784 
 2012 9.065395 
 2013 9.451399 
 2014 8.741123 
 2015 9.246153 
 2016 9.610161 
 2017 9.063374 
 2018 9.845124