# year    value 
 1980 21.67002 
 1981 21.92825 
 1982 21.57737 
 1983 21.78814 
 1984 21.72144 
 1985 21.64987 
 1986  21.6269 
 1987 21.74323 
 1988  21.9882 
 1989 21.52962 
 1990 21.81025 
 1991 21.93002 
 1992 21.39292 
 1993  21.3744 
 1994 21.98528 
 1995 22.05748 
 1996  21.5928 
 1997 21.97749 
 1998 22.25355 
 1999 22.03003 
 2000 22.13461 
 2001 22.08937 
 2002 22.30508 
 2003 21.89369 
 2004  21.8891 
 2005 22.41537 
 2006  22.3949 
 2007 22.36213 
 2008 22.13195 
 2009 22.30497 
 2010 22.52256 
 2011 22.36014 
 2012 22.39307 
 2013 22.35795 
 2014 22.24924 
 2015 22.18653 
 2016 22.62453 
 2017 22.50738 
 2018 22.65259