# year    value 
 1980  16.2188 
 1981 16.21848 
 1982 15.97821 
 1983 15.82808 
 1984 15.93888 
 1985 16.10343 
 1986 16.27468 
 1987 15.97022 
 1988 16.40738 
 1989 16.16927 
 1990 16.45853 
 1991 16.45642 
 1992 15.84609 
 1993 15.70122 
 1994 16.86247 
 1995  16.4194 
 1996 16.35982 
 1997 16.41175 
 1998 16.91776 
 1999 16.63832 
 2000 16.93086 
 2001 16.97254 
 2002 16.94116 
 2003 16.78061 
 2004 16.59192 
 2005 16.88681 
 2006 17.08519 
 2007 17.12109 
 2008 16.99453 
 2009 16.64022 
 2010 17.11801 
 2011 17.00056 
 2012 17.17716 
 2013 17.09703 
 2014 16.91829 
 2015 17.30745 
 2016  17.3266 
 2017 17.40203 
 2018 17.44021