# year    value 
 1979 9.121117 
 1980  8.79634 
 1981 8.646888 
 1982 8.475664 
 1983 8.356739 
 1984 7.884068 
 1985 9.136991 
 1986 8.748174 
 1987 8.946629 
 1988 8.708045 
 1989 8.672194 
 1990 8.814423 
 1991 8.563593 
 1992 8.143184 
 1993 8.811806 
 1994 8.798196 
 1995 8.260023 
 1996   8.6708 
 1997 8.845821 
 1998 9.392454 
 1999 8.979602 
 2000 8.466036 
 2001 8.881341 
 2002 8.690596 
 2003 8.963764 
 2004 9.056283 
 2005 9.116935 
 2006 9.057042 
 2007 8.115711 
 2008 8.799767 
 2009 9.176319 
 2010 8.496695 
 2011 8.668941 
 2012  8.65842 
 2013 9.232328 
 2014 9.329539 
 2015 9.253313 
 2016 9.019143 
 2017 9.354444 
 2018  8.72426