# year    value 
 1980  19.9629 
 1981 19.70309 
 1982 19.95358 
 1983 20.10446 
 1984 19.57122 
 1985 19.85999 
 1986 19.94643 
 1987 20.27297 
 1988 19.89423 
 1989 19.86916 
 1990 19.84993 
 1991 20.03533 
 1992 19.94382 
 1993  19.9648 
 1994 20.32873 
 1995 20.15625 
 1996 19.80836 
 1997 20.41166 
 1998 20.31798 
 1999 19.64775 
 2000 19.73729 
 2001 19.93387 
 2002 20.05278 
 2003 20.10545 
 2004 20.16056 
 2005 19.98792 
 2006 20.22546 
 2007 19.64512 
 2008 19.94315 
 2009 20.24658 
 2010  20.0948 
 2011 20.03436 
 2012 20.27954 
 2013   20.082 
 2014 20.33793 
 2015 20.64013 
 2016  20.3109 
 2017 20.41065 
 2018 20.08675