# year    value 
 1980 24.70076 
 1981 24.51708 
 1982 24.42949 
 1983 24.57151 
 1984 24.47091 
 1985 24.51267 
 1986 24.49063 
 1987 24.93884 
 1988 24.70531 
 1989 24.39383 
 1990 24.80469 
 1991 24.65651 
 1992 24.36217 
 1993 24.64161 
 1994 24.63415 
 1995 24.76655 
 1996 24.76069 
 1997 24.77065 
 1998  25.2445 
 1999 24.85735 
 2000  24.7705 
 2001 25.00361 
 2002 25.11855 
 2003 25.13197 
 2004  25.0785 
 2005 25.15119 
 2006 25.10161 
 2007 25.04972 
 2008 24.89175 
 2009 25.32565 
 2010 25.48981 
 2011 25.02162 
 2012 25.04549 
 2013 25.06285 
 2014 25.09705 
 2015 25.23277 
 2016 25.41866 
 2017 25.22142 
 2018 25.13853