# year    value 
 1979 19.74068 
 1980  19.9074 
 1981 19.94637 
 1982  19.9518 
 1983 20.54137 
 1984 19.81132 
 1985 19.70144 
 1986 19.69974 
 1987 20.17013 
 1988  20.4877 
 1989  19.6838 
 1990 19.94873 
 1991 20.24665 
 1992 20.05326 
 1993 19.84143 
 1994 20.26945 
 1995 20.35007 
 1996 20.05695 
 1997 20.02977 
 1998 21.03385 
 1999 20.20872 
 2000 19.94381 
 2001 20.04443 
 2002 20.20016 
 2003 20.65393 
 2004 20.34467 
 2005 20.61914 
 2006 20.50916 
 2007 20.58705 
 2008 20.03872 
 2009 20.22671 
 2010 20.98746 
 2011 20.24089 
 2012 20.20093 
 2013 20.63671 
 2014 20.50752 
 2015 20.65215 
 2016 21.37982 
 2017 20.88613 
 2018 20.51952 
 2019 20.98253