# year    value 
 1980 8.215761 
 1981  8.89185 
 1982 8.168846 
 1983 8.403955 
 1984 8.423326 
 1985 8.223839 
 1986 8.384639 
 1987 8.221688 
 1988 8.571279 
 1989  8.74291 
 1990 9.181573 
 1991 8.506152 
 1992 8.654161 
 1993 8.665473 
 1994 8.870536 
 1995 8.668411 
 1996 8.516462 
 1997 8.918065 
 1998 9.113577 
 1999 8.555667 
 2000  9.15688 
 2001 9.039847 
 2002 9.161016 
 2003 8.941149 
 2004 9.179352 
 2005 9.175053 
 2006 8.848988 
 2007 9.317218 
 2008 9.353939 
 2009 9.170661 
 2010 9.065016 
 2011 9.101787 
 2012 9.088073 
 2013 9.136641 
 2014 9.394643 
 2015 9.466345 
 2016 9.847066 
 2017 9.643838 
 2018 9.642357