# year    value 
 1980 8.373754 
 1981 9.003172 
 1982 8.248755 
 1983 8.518387 
 1984 8.693846 
 1985  8.37532 
 1986 8.478269 
 1987 8.404255 
 1988 8.798879 
 1989 8.863844 
 1990 9.286829 
 1991 8.665413 
 1992 8.702878 
 1993 8.783064 
 1994 9.080572 
 1995  8.75627 
 1996 8.635443 
 1997  8.92965 
 1998 9.265338 
 1999 8.737667 
 2000 9.272566 
 2001 9.170069 
 2002 9.289266 
 2003 9.066793 
 2004 9.344133 
 2005 9.364727 
 2006 8.979483 
 2007  9.54763 
 2008 9.491558 
 2009 9.319495 
 2010 9.330353 
 2011 9.200692 
 2012 9.246549 
 2013 9.413495 
 2014 9.702799 
 2015 9.716844 
 2016 10.26709 
 2017  9.92381 
 2018 9.878729