# year    value 
 1980 9.228687 
 1981 10.41984 
 1982 8.840969 
 1983 8.504516 
 1984 9.326756 
 1985 10.53096 
 1986 10.88564 
 1987  10.6405 
 1988 10.11586 
 1989 10.44931 
 1990  10.1231 
 1991 9.575826 
 1992 11.27812 
 1993 9.976453 
 1994 10.93255 
 1995  8.95628 
 1996 9.499295 
 1997 9.242358 
 1998  9.22796 
 1999 9.221407 
 2000 10.79308 
 2001 10.20322 
 2002 8.697449 
 2003 9.921587 
 2004 11.07529 
 2005 10.06356 
 2006 10.71908 
 2007 10.83438 
 2008 9.220631 
 2009 9.732819 
 2010 9.528361 
 2011 9.289131 
 2012  11.6985 
 2013 9.534122 
 2014 10.16607 
 2015 10.82707 
 2016 11.04977 
 2017 10.90167 
 2018 10.58393