# year    value 
 1979 21.93216 
 1980 21.44559 
 1981 20.98605 
 1982  21.2933 
 1983 20.80972 
 1984 20.88641 
 1985 21.35745 
 1986 21.21891 
 1987 21.36392 
 1988 21.86316 
 1989 20.64536 
 1990 21.55524 
 1991 21.88058 
 1992 20.89983 
 1993 21.06792 
 1994 21.58859 
 1995 21.22545 
 1996 21.87469 
 1997 21.39789 
 1998 21.96835 
 1999 21.83799 
 2000   21.242 
 2001 21.39266 
 2002  21.8267 
 2003 22.07116 
 2004 21.87145 
 2005 21.95706 
 2006 22.25671 
 2007 21.76282 
 2008 21.35083 
 2009 22.10675 
 2010  22.8468 
 2011 21.86366 
 2012 21.41454 
 2013 22.15575 
 2014 21.84363 
 2015 21.90202 
 2016 22.17892 
 2017 22.29769 
 2018 22.13808 
 2019 22.06874