# year    value 
 1980 5.034388 
 1981 7.368557 
 1982 6.105238 
 1983 6.840795 
 1984  4.94222 
 1985 6.211272 
 1986 6.827294 
 1987 4.851473 
 1988 6.737193 
 1989 7.745622 
 1990 7.710277 
 1991 6.072333 
 1992 7.339474 
 1993 7.260576 
 1994 7.738591 
 1995 6.426353 
 1996 6.276014 
 1997 7.136886 
 1998 7.142179 
 1999 7.876578 
 2000 8.335958 
 2001 7.933861 
 2002 7.827193 
 2003  8.03212 
 2004 6.381857 
 2005 7.049664 
 2006  6.68971 
 2007 9.004604 
 2008 7.290442 
 2009 8.443166 
 2010 6.822637 
 2011 8.754848 
 2012 8.299072 
 2013 6.474652 
 2014 8.346631 
 2015 7.871954 
 2016 7.352166 
 2017 8.529776 
 2018  8.65164