# year    value 
 1979 22.61559 
 1980 22.53574 
 1981 22.53044 
 1982 22.86628 
 1983 22.74016 
 1984  22.6504 
 1985 22.56335 
 1986 22.47003 
 1987 23.15075 
 1988  22.9918 
 1989 22.78305 
 1990 22.87676 
 1991 22.61193 
 1992 22.27735 
 1993 22.64804 
 1994 23.20304 
 1995 23.23905 
 1996 22.79886 
 1997 23.75655 
 1998 22.96417 
 1999 23.13588 
 2000 22.60221 
 2001 22.92916 
 2002  23.4401 
 2003 23.39777 
 2004  23.3065 
 2005 22.97815 
 2006 23.49371 
 2007 23.28156 
 2008 23.49925 
 2009 23.71428 
 2010 23.40454 
 2011 23.68697 
 2012 23.84238 
 2013 23.16728 
 2014 23.77657 
 2015 23.71526 
 2016 23.29391 
 2017 23.35675 
 2018 23.55089