# year    value 
 1980 16.50413 
 1981 16.86673 
 1982   16.295 
 1983 16.37268 
 1984 16.64599 
 1985 16.47639 
 1986 16.48192 
 1987 16.47883 
 1988 16.93178 
 1989 16.25189 
 1990 16.83204 
 1991 16.80172 
 1992 16.19163 
 1993 16.37278 
 1994 17.12203 
 1995 16.96865 
 1996 16.60626 
 1997 16.83522 
 1998 17.24023 
 1999  16.9383 
 2000 17.04809 
 2001 17.12785 
 2002 17.18423 
 2003 16.84184 
 2004 16.56089 
 2005  17.0706 
 2006 17.41755 
 2007 17.19576 
 2008 17.03975 
 2009 17.01794 
 2010 17.35383 
 2011 17.18957 
 2012  17.1868 
 2013  17.5414 
 2014 17.11732 
 2015 16.99742 
 2016 17.74133 
 2017 17.48993 
 2018 17.83521