# year    value 
 1979 19.37156 
 1980 19.25734 
 1981 19.24421 
 1982 19.63264 
 1983 19.36228 
 1984  19.3721 
 1985 19.30525 
 1986 19.21936 
 1987 19.82511 
 1988 19.64119 
 1989 19.47494 
 1990 19.62876 
 1991 19.34886 
 1992 19.06407 
 1993 19.40866 
 1994 19.98682 
 1995 19.99288 
 1996 19.53111 
 1997 20.41096 
 1998  19.7067 
 1999 19.76302 
 2000 19.38374 
 2001  19.7159 
 2002 20.12734 
 2003  20.1704 
 2004 20.04473 
 2005 19.53653 
 2006 20.21193 
 2007 19.96645 
 2008 20.16508 
 2009 20.41462 
 2010 20.02163 
 2011 20.33931 
 2012 20.59809 
 2013 19.88162 
 2014 20.49281 
 2015 20.32475 
 2016 20.08543 
 2017 20.10168 
 2018 20.35284