# year    value 
 1980 7.531713 
 1981 8.583408 
 1982 7.261358 
 1983 7.218756 
 1984 8.040033 
 1985 8.441037 
 1986 9.208495 
 1987 9.048939 
 1988 8.406953 
 1989 9.363457 
 1990 8.873096 
 1991 7.102961 
 1992 10.21511 
 1993 8.841952 
 1994 9.602945 
 1995 7.744568 
 1996 8.685993 
 1997 8.433998 
 1998 7.410634 
 1999 7.325625 
 2000 9.126102 
 2001 8.906606 
 2002 7.570121 
 2003 8.409986 
 2004 9.763954 
 2005 8.577783 
 2006 8.738653 
 2007 9.379926 
 2008 7.674598 
 2009 8.428896 
 2010 7.433463 
 2011 7.537966 
 2012 9.409396 
 2013 8.812896 
 2014 9.166613 
 2015 9.474968 
 2016 9.532142 
 2017 9.398401 
 2018 9.355001