# year    value 
 1980 23.61654 
 1981 23.49079 
 1982 23.55801 
 1983 23.86693 
 1984 23.30384 
 1985  23.2854 
 1986 23.44248 
 1987 23.77571 
 1988 23.56896 
 1989   23.477 
 1990 23.66239 
 1991 23.54321 
 1992 23.51337 
 1993 23.65424 
 1994 23.64395 
 1995 23.75783 
 1996  23.5496 
 1997 23.79733 
 1998 24.15497 
 1999 23.51828 
 2000 23.64115 
 2001 23.71974 
 2002 23.92301 
 2003 23.87795 
 2004 23.68953 
 2005 23.97143 
 2006 23.98159 
 2007 23.76103 
 2008 23.63052 
 2009  24.2707 
 2010 24.00468 
 2011 24.12034 
 2012 23.94353 
 2013 23.97814 
 2014 24.13387 
 2015 24.18944 
 2016   24.226 
 2017 24.14643 
 2018 24.10462