# year    value 
 1980 15.25571 
 1981 14.98407 
 1982 15.17503 
 1983  15.1556 
 1984 14.85329 
 1985  15.1137 
 1986  14.6751 
 1987 15.07362 
 1988 15.18189 
 1989 15.03998 
 1990 15.35043 
 1991 15.06635 
 1992 14.18004 
 1993 14.85082 
 1994 15.11984 
 1995 15.05751 
 1996 15.16624 
 1997 15.12809 
 1998 15.07318 
 1999 15.35952 
 2000 14.91172 
 2001 14.84315 
 2002 15.38017 
 2003 15.12944 
 2004 15.26515 
 2005 15.08502 
 2006 15.81433 
 2007 15.55491 
 2008 15.61724 
 2009 15.24401 
 2010 14.98422 
 2011 15.61755 
 2012  15.7943 
 2013 15.52937 
 2014 16.11341 
 2015 15.26497 
 2016 15.05501 
 2017 15.67069 
 2018 15.49658