# year    value 
 1980 7.078714 
 1981 9.411821 
 1982 8.148686 
 1983  8.93313 
 1984 7.053294 
 1985 8.276267 
 1986 8.818941 
 1987 6.885804 
 1988 8.752639 
 1989 9.798386 
 1990 9.763118 
 1991 8.102919 
 1992 9.388586 
 1993 9.319204 
 1994 9.747515 
 1995 8.459103 
 1996 8.269896 
 1997  9.10321 
 1998 9.180304 
 1999 9.907219 
 2000  10.3798 
 2001 9.951436 
 2002 9.883068 
 2003 10.05341 
 2004 8.433072 
 2005 9.050919 
 2006 8.707464 
 2007 11.03552 
 2008 9.355375 
 2009 10.47408 
 2010 8.893717 
 2011 10.74334 
 2012 10.33216 
 2013 8.482801 
 2014 10.40857 
 2015  9.87748 
 2016 9.399471 
 2017  10.5531 
 2018 10.71112