# year    value 
 1979 8.403299 
 1980 8.070675 
 1981 7.741349 
 1982 8.387019 
 1983 7.562335 
 1984 7.053769 
 1985 7.674119 
 1986 7.969343 
 1987 8.148735 
 1988 7.960224 
 1989 8.075067 
 1990 7.827855 
 1991 8.004616 
 1992 7.330484 
 1993 7.983235 
 1994 8.467272 
 1995 8.704691 
 1996 7.932251 
 1997 8.693789 
 1998 8.751297 
 1999 7.778868 
 2000 7.623386 
 2001 8.288006 
 2002 7.634812 
 2003 8.454993 
 2004   8.2069 
 2005 8.767688 
 2006 8.970096 
 2007 7.543066 
 2008 8.416265 
 2009 8.253706 
 2010  8.20795 
 2011 7.989505 
 2012 8.585772 
 2013 8.127256 
 2014 8.685793 
 2015  9.21164 
 2016 8.555674 
 2017 8.705541 
 2018 7.826601