# year    value 
 1980  23.9384 
 1981 23.68481 
 1982 23.81754 
 1983 24.07713 
 1984 23.86755 
 1985 23.88417 
 1986 23.80353 
 1987 24.34501 
 1988 24.19537 
 1989 23.85743 
 1990   24.241 
 1991 24.08127 
 1992 23.75849 
 1993 24.02019 
 1994 24.23861 
 1995 24.39287 
 1996  24.1049 
 1997 24.56544 
 1998  24.3683 
 1999 23.96793 
 2000 24.10601 
 2001 24.07917 
 2002  24.5276 
 2003 24.40455 
 2004 24.42068 
 2005 24.47661 
 2006 24.38209 
 2007 24.46671 
 2008 24.43181 
 2009 24.58779 
 2010 24.26755 
 2011 24.17842 
 2012 24.62014 
 2013 24.48781 
 2014 24.73999 
 2015 24.88142 
 2016 24.44159 
 2017 24.53001 
 2018 24.54589