# year    value 
 1980 21.01892 
 1981 20.55399 
 1982 20.47766 
 1983 20.56359 
 1984 20.86764 
 1985 20.58414 
 1986 20.58853 
 1987 20.61814 
 1988 20.86385 
 1989 20.46563 
 1990 20.54869 
 1991 21.00468 
 1992 20.62893 
 1993 20.51988 
 1994 20.90075 
 1995 20.92488 
 1996 20.68562 
 1997 20.52992 
 1998 21.45046 
 1999  21.0856 
 2000 20.96639 
 2001 21.08389 
 2002  21.3931 
 2003 21.31938 
 2004 21.30971 
 2005  21.1986 
 2006 21.15876 
 2007 21.20738 
 2008 21.13727 
 2009 21.27728 
 2010 21.66882 
 2011  21.0666 
 2012 21.27049 
 2013 21.37852 
 2014 21.23746 
 2015 21.33693 
 2016 21.73092 
 2017 21.24135 
 2018  21.4132