# year    value 
 1979 6.217147 
 1980  5.37685 
 1981 5.727897 
 1982 5.435159 
 1983 5.237793 
 1984 3.792818 
 1985 4.379541 
 1986 5.243681 
 1987 6.219606 
 1988 5.631233 
 1989 5.699066 
 1990 6.157114 
 1991 5.518689 
 1992 5.767904 
 1993 6.036659 
 1994 5.121621 
 1995 5.859299 
 1996 5.096588 
 1997 5.871185 
 1998 5.615756 
 1999  7.00435 
 2000 5.586066 
 2001   5.9973 
 2002 6.843706 
 2003 5.624135 
 2004 6.499045 
 2005 5.122853 
 2006 5.708311 
 2007 6.816297 
 2008  4.14275 
 2009 6.908549 
 2010 5.871917 
 2011 4.902705 
 2012 4.082524 
 2013 5.321228 
 2014  5.35034 
 2015 6.405154 
 2016 6.538153 
 2017 6.997062 
 2018 5.699594 
 2019 5.632968