# year    value 
 1980 7.632801 
 1981 7.867605 
 1982 7.317289 
 1983  7.65121 
 1984   7.7888 
 1985 7.477737 
 1986 7.206899 
 1987 7.279262 
 1988 8.119273 
 1989  7.97977 
 1990 8.312925 
 1991 8.424637 
 1992  7.04037 
 1993 7.917585 
 1994 8.097969 
 1995 8.167635 
 1996 7.546225 
 1997 8.028769 
 1998 8.635311 
 1999  7.75918 
 2000 8.078775 
 2001 8.506304 
 2002 8.431825 
 2003 8.592057 
 2004 8.018384 
 2005 8.454182 
 2006 8.452615 
 2007 8.664599 
 2008 8.249965 
 2009 8.219307 
 2010 8.536912 
 2011 8.614388 
 2012 8.648458 
 2013 8.727873 
 2014 8.538341 
 2015 8.333937 
 2016 9.139276 
 2017 8.470943 
 2018 8.364129