# year    value 
 1979 8.746857 
 1980 7.535843 
 1981  9.88614 
 1982 8.451137 
 1983 9.350309 
 1984 7.460972 
 1985 8.718656 
 1986 9.292869 
 1987 7.333708 
 1988 9.202238 
 1989 10.17058 
 1990 10.10389 
 1991 8.394316 
 1992  9.67914 
 1993 9.589313 
 1994 10.16627 
 1995 8.833615 
 1996 8.662841 
 1997 9.504925 
 1998 9.549719 
 1999 10.24634 
 2000 10.72822 
 2001 10.52437 
 2002 10.27813 
 2003 10.41478 
 2004 8.882326 
 2005 9.541548 
 2006 9.324383 
 2007 11.59406 
 2008 9.934079 
 2009 10.94536 
 2010 9.371827 
 2011 11.08712 
 2012 10.67979 
 2013 8.953737 
 2014 10.73096 
 2015 10.35389 
 2016 9.877858 
 2017 11.00528 
 2018 11.14094