# year    value 
 1980 15.03792 
 1981 14.82369 
 1982 14.91624 
 1983  15.7609 
 1984 14.97363 
 1985 14.45808 
 1986 14.95255 
 1987 15.63315 
 1988 15.18199 
 1989 15.41331 
 1990 15.10116 
 1991 14.99383 
 1992 14.94631 
 1993 15.00513 
 1994 15.08967 
 1995 15.45681 
 1996 15.00292 
 1997 14.75275 
 1998 15.74973 
 1999 15.06435 
 2000 14.68213 
 2001 15.23848 
 2002  14.8382 
 2003  15.2704 
 2004 15.21245 
 2005 15.49205 
 2006 15.01748 
 2007 15.30369 
 2008 14.74189 
 2009 15.10145 
 2010 15.55697 
 2011 14.77403 
 2012 15.12665 
 2013 15.32218 
 2014 15.30523 
 2015   15.091 
 2016 16.01388 
 2017 15.89625 
 2018 15.14108