# year    value 
 1979 8.547754 
 1980 9.166908 
 1981 8.988365 
 1982 8.820882 
 1983 9.306874 
 1984 8.876143 
 1985 8.584656 
 1986 8.794083 
 1987 8.786808 
 1988 9.326762 
 1989 9.424839 
 1990 9.683562 
 1991  10.0435 
 1992 8.478106 
 1993 9.198184 
 1994 9.566158 
 1995 9.381241 
 1996 8.336493 
 1997 9.584779 
 1998 9.506603 
 1999 9.005286 
 2000 8.886641 
 2001 9.732339 
 2002 9.684431 
 2003 9.643084 
 2004 9.513472 
 2005 9.771169 
 2006 9.814687 
 2007  10.1796 
 2008  9.49362 
 2009 9.887986 
 2010 10.12792 
 2011 9.846418 
 2012 9.985841 
 2013 10.24636 
 2014 9.930734 
 2015 9.861896 
 2016 10.68262 
 2017 9.898746 
 2018 10.01242