# year    value 
 1979 7.187479 
 1980 7.124923 
 1981 8.158888 
 1982 7.460381 
 1983 7.707475 
 1984  7.42035 
 1985 7.558112 
 1986 8.017314 
 1987 7.399175 
 1988 7.863533 
 1989 7.996211 
 1990   8.6186 
 1991 8.005145 
 1992 7.514942 
 1993 7.650354 
 1994 7.961853 
 1995 8.163091 
 1996 6.962389 
 1997 8.019449 
 1998  8.35024 
 1999  8.16747 
 2000  9.00714 
 2001 9.046963 
 2002 8.074625 
 2003 7.800497 
 2004 8.391088 
 2005 8.573391 
 2006 8.880839 
 2007 8.837377 
 2008  9.05648 
 2009 8.253708 
 2010  8.72687 
 2011 8.294096 
 2012 9.503684 
 2013 8.247268 
 2014 8.614548 
 2015 8.809766 
 2016 9.405679 
 2017 8.999166 
 2018 8.721569