# year    value 
 1980 6.552144 
 1981 7.182643 
 1982 7.814019 
 1983 7.756811 
 1984 6.872021 
 1985 6.923011 
 1986 7.258727 
 1987 7.113452 
 1988 7.853188 
 1989 7.987933 
 1990   8.1476 
 1991 7.292819 
 1992 8.114198 
 1993  7.66535 
 1994 8.813594 
 1995 7.758123 
 1996 7.073145 
 1997 8.111614 
 1998 8.030347 
 1999 8.086094 
 2000 8.721308 
 2001 8.043513 
 2002 8.615994 
 2003 8.378711 
 2004 7.861689 
 2005 7.524736 
 2006 8.333976 
 2007 8.647461 
 2008  8.38001 
 2009 8.462286 
 2010 7.458574 
 2011 8.852525 
 2012  8.50233 
 2013 8.127648 
 2014 9.208764 
 2015 9.099698 
 2016 8.673236 
 2017 8.665361 
 2018 9.402266