# year    value 
 1980 8.301144 
 1981 8.035849 
 1982 7.869842 
 1983  8.28119 
 1984 7.960998 
 1985 7.675438 
 1986 7.876569 
 1987 7.822017 
 1988 8.364345 
 1989 8.374741 
 1990 8.836219 
 1991  8.99012 
 1992 7.769661 
 1993 8.371855 
 1994 8.590878 
 1995 8.678571 
 1996 7.887885 
 1997 8.934085 
 1998 8.874684 
 1999 8.220407 
 2000 8.256161 
 2001  8.89238 
 2002 8.955803 
 2003 8.962397 
 2004 8.651556 
 2005 8.866697 
 2006 8.811387 
 2007 9.225082 
 2008 8.589622 
 2009 8.765306 
 2010 9.032208 
 2011 8.970676 
 2012  8.77796 
 2013 9.035367 
 2014 8.929162 
 2015 8.962414 
 2016 9.378416 
 2017 8.918233 
 2018 8.873106