# year    value 
 1980 20.05393 
 1981  20.4489 
 1982 19.81404 
 1983 20.45217 
 1984 20.20612 
 1985 19.90503 
 1986 19.95992 
 1987 20.07396 
 1988 20.80157 
 1989 20.40993 
 1990 20.36065 
 1991 20.58378 
 1992 19.38973 
 1993  19.8496 
 1994 20.48919 
 1995 20.78579 
 1996 20.31011 
 1997 20.46799 
 1998 21.12044 
 1999 20.89582 
 2000 20.66528 
 2001 20.88019 
 2002 20.79694 
 2003 20.76021 
 2004 20.21475 
 2005 20.96593 
 2006 21.20488 
 2007 21.06482 
 2008 21.00169 
 2009 20.43278 
 2010  21.6722 
 2011 21.24619 
 2012 21.65121 
 2013  20.9272 
 2014 20.90488 
 2015 21.10014 
 2016 21.44963 
 2017 21.14904 
 2018 21.35622