# year    value 
 1980 20.83661 
 1981  21.1904 
 1982 20.85501 
 1983 21.20668 
 1984 20.82156 
 1985 20.51882 
 1986 20.42029 
 1987 20.66899 
 1988  20.6502 
 1989 21.23165 
 1990 21.02869 
 1991 20.96016 
 1992 20.16544 
 1993 20.54667 
 1994 20.35747 
 1995 21.03923 
 1996 20.49794 
 1997 20.91342 
 1998 20.59978 
 1999 21.20316 
 2000 20.68052 
 2001 21.51268 
 2002 20.14735 
 2003 21.12799 
 2004 21.03289 
 2005   20.927 
 2006 21.04604 
 2007 21.14251 
 2008 21.05634 
 2009 21.37527 
 2010 21.13305 
 2011   21.151 
 2012 21.22242 
 2013 21.43975 
 2014 21.55798 
 2015 21.15906 
 2016 21.64073 
 2017 21.53574 
 2018  21.7701