# year    value 
 1980 7.021142 
 1981  8.12596 
 1982  7.39748 
 1983  7.59526 
 1984 7.302799 
 1985 7.517445 
 1986 8.013374 
 1987 7.353836 
 1988  7.82022 
 1989 7.920485 
 1990 8.572207 
 1991 7.978544 
 1992 7.501132 
 1993 7.623241 
 1994 7.978971 
 1995 8.060055 
 1996 6.828868 
 1997 7.876587 
 1998 8.310423 
 1999   8.0995 
 2000 8.904014 
 2001 8.899119 
 2002 7.978405 
 2003 7.700759 
 2004 8.305643 
 2005 8.358638 
 2006 8.752166 
 2007 8.738306 
 2008  8.86867 
 2009 8.144857 
 2010 8.608642 
 2011 8.182921 
 2012 9.360821 
 2013 8.026183 
 2014  8.42891 
 2015  8.70095 
 2016 9.283405 
 2017 8.874136 
 2018 8.543891