# year    value 
 1979  23.9404 
 1980 24.47282 
 1981 24.20908 
 1982 23.90482 
 1983 24.54286 
 1984 24.02186 
 1985 24.08955 
 1986 24.38481 
 1987 24.50514 
 1988 24.43486 
 1989 23.87801 
 1990 24.48462 
 1991 24.32341 
 1992 24.58158 
 1993 24.45891 
 1994 24.24846 
 1995 24.14101 
 1996 24.22721 
 1997 23.95012 
 1998 25.05863 
 1999 24.14637 
 2000 23.76511 
 2001 24.05152 
 2002 24.78144 
 2003 24.48717 
 2004 24.32623 
 2005 24.89116 
 2006 23.95429 
 2007 24.61459 
 2008 24.03538 
 2009 24.43305 
 2010 24.83989 
 2011 23.97168 
 2012 24.22943 
 2013 24.70432 
 2014 24.59829 
 2015 24.57821 
 2016 25.25235 
 2017 24.75281 
 2018 24.74777