# year    value 
 1979 7.872217 
 1980 7.465603 
 1981 8.681914 
 1982 7.337902 
 1983 7.174535 
 1984 8.200247 
 1985 8.572155 
 1986 9.348752 
 1987 9.089653 
 1988 8.536414 
 1989 9.770171 
 1990 9.042537 
 1991 7.099937 
 1992 10.44366 
 1993 9.027207 
 1994 9.556131 
 1995 7.419958 
 1996 8.542868 
 1997 8.710205 
 1998 7.118205 
 1999 7.365917 
 2000 9.461229 
 2001 9.168755 
 2002 8.144143 
 2003 8.508085 
 2004 10.08026 
 2005 8.791337 
 2006 8.962328 
 2007 9.933934 
 2008 7.756037 
 2009 8.867992 
 2010 7.461947 
 2011 7.666296 
 2012 9.868984 
 2013 9.397997 
 2014 9.451567 
 2015 9.882282 
 2016 9.871179 
 2017 9.793749 
 2018 9.833715