# year    value 
 1980 8.887056 
 1981 7.826676 
 1982  8.35591 
 1983 8.821888 
 1984 8.157285 
 1985 8.049422 
 1986 8.009146 
 1987 8.543571 
 1988 8.795002 
 1989 8.668389 
 1990 9.042383 
 1991 8.286862 
 1992 7.849856 
 1993 8.135681 
 1994 8.516854 
 1995   8.8009 
 1996 8.392829 
 1997 7.972633 
 1998 9.577878 
 1999  9.18451 
 2000 8.324039 
 2001 9.157954 
 2002 8.705742 
 2003 8.941651 
 2004 8.618276 
 2005 9.254302 
 2006 9.519469 
 2007 8.927238 
 2008  9.06284 
 2009 8.974751 
 2010 9.238266 
 2011 9.159009 
 2012 8.424299 
 2013 8.929507 
 2014 9.158115 
 2015 9.156549 
 2016 9.168956 
 2017 9.361703 
 2018 8.507871