# year    value 
 1980 9.214519 
 1981 8.869777 
 1982 9.410985 
 1983 9.219312 
 1984 8.511198 
 1985 9.103778 
 1986 9.413555 
 1987 9.907761 
 1988 8.693892 
 1989 9.307127 
 1990 9.011456 
 1991  9.41125 
 1992 9.163609 
 1993 9.524619 
 1994 9.761219 
 1995  9.38111 
 1996 8.788301 
 1997 10.20166 
 1998 10.00362 
 1999  8.83086 
 2000 8.862202 
 2001 9.234708 
 2002 8.966185 
 2003  9.10063 
 2004 9.205875 
 2005 9.444262 
 2006 9.943851 
 2007 8.073212 
 2008 9.334017 
 2009 9.290648 
 2010 8.773096 
 2011 9.189012 
 2012 9.365023 
 2013 8.941306 
 2014 9.863275 
 2015 10.22765 
 2016 9.449032 
 2017 9.781899 
 2018 8.527918