# year    value 
 1980 24.15379 
 1981 23.93533 
 1982 23.96408 
 1983 24.30612 
 1984 23.86328 
 1985 23.89464 
 1986 24.00983 
 1987 24.34873 
 1988 24.26417 
 1989 23.89983 
 1990 24.23967 
 1991  24.1685 
 1992 24.10164 
 1993 24.14228 
 1994  24.1509 
 1995 24.26873 
 1996 24.18863 
 1997 24.25298 
 1998 24.72532 
 1999 24.07967 
 2000 23.86781 
 2001 24.09236 
 2002 24.50956 
 2003 24.46723 
 2004 24.31597 
 2005 24.71011 
 2006 24.31108 
 2007 24.43828 
 2008  24.2837 
 2009 24.50995 
 2010 24.55835 
 2011  24.1342 
 2012 24.39595 
 2013 24.67293 
 2014 24.60037 
 2015 24.89618 
 2016  24.9376 
 2017 24.75401 
 2018 24.66998