# year    value 
 1980 7.707079 
 1981 8.129369 
 1982  9.40627 
 1983 8.167122 
 1984 8.500359 
 1985  8.07509 
 1986 8.800855 
 1987 9.633487 
 1988 7.929834 
 1989 7.952329 
 1990 8.452211 
 1991 8.465676 
 1992 8.387602 
 1993 7.323527 
 1994 9.172878 
 1995 8.189665 
 1996 7.610372 
 1997 8.777164 
 1998 7.519367 
 1999  8.81098 
 2000 9.543548 
 2001  8.21668 
 2002 8.784986 
 2003 8.269821 
 2004 9.156614 
 2005 8.873271 
 2006 10.73853 
 2007 7.397082 
 2008 8.439035 
 2009 9.499186 
 2010  8.03589 
 2011 9.754057 
 2012 9.629372 
 2013 9.192065 
 2014 10.46792 
 2015 9.039919 
 2016 9.106906 
 2017 8.352505 
 2018 10.39412