# year    value 
 1980 7.571723 
 1981 7.306008 
 1982 7.358559 
 1983 8.022329 
 1984 7.000632 
 1985  6.83294 
 1986 6.967304 
 1987 7.100062 
 1988 7.756977 
 1989 7.557698 
 1990 8.099083 
 1991   7.6498 
 1992 7.045238 
 1993 6.473069 
 1994  8.18156 
 1995 7.928555 
 1996 7.012037 
 1997 7.507891 
 1998  7.93812 
 1999 8.065357 
 2000 7.145411 
 2001 8.333234 
 2002 7.665205 
 2003 7.928533 
 2004 8.349347 
 2005 8.683784 
 2006 8.240226 
 2007 8.189932 
 2008 8.344511 
 2009 8.055293 
 2010 8.508097 
 2011 8.159076 
 2012 8.183402 
 2013 8.407548 
 2014   7.9259 
 2015 8.389146 
 2016 8.005039 
 2017 8.290092 
 2018 7.963048