# year    value 
 1980 16.11231 
 1981 15.83092 
 1982 15.77574 
 1983 15.38938 
 1984 14.85204 
 1985 15.50913 
 1986 15.47669 
 1987  15.2445 
 1988  15.4438 
 1989 15.66778 
 1990 15.44706 
 1991 15.90625 
 1992 15.49964 
 1993 15.65827 
 1994 15.76422 
 1995 15.07588 
 1996 15.56341 
 1997 15.59866 
 1998 15.66796 
 1999 15.38601 
 2000 15.27903 
 2001 15.27756 
 2002 15.67817 
 2003 15.69184 
 2004 15.47795 
 2005 15.70319 
 2006 15.04862 
 2007 15.63701 
 2008 15.58562 
 2009 16.08337 
 2010 15.88528 
 2011 15.52485 
 2012  15.6278 
 2013 15.91682 
 2014 15.72479 
 2015 15.99291 
 2016 15.84252 
 2017 15.99507 
 2018 16.41313