# year    value 
 1980 16.19751 
 1981 16.14884 
 1982 15.85421 
 1983 15.65992 
 1984 15.88908 
 1985 16.09809 
 1986 16.22115 
 1987 15.91243 
 1988  16.4421 
 1989 16.09591 
 1990 16.47121 
 1991 16.42587 
 1992 15.72911 
 1993 15.75253 
 1994 17.01656 
 1995 16.37542 
 1996 16.36806 
 1997 16.37544 
 1998 17.00832 
 1999 16.61175 
 2000 16.98879 
 2001 17.08285 
 2002 17.07933 
 2003 16.86671 
 2004 16.55392 
 2005 16.85218 
 2006 17.14806 
 2007 17.16287 
 2008 17.09052 
 2009 16.55031 
 2010 17.20505 
 2011 17.00932 
 2012 17.26959 
 2013 17.16149 
 2014 16.94573 
 2015 17.33204 
 2016 17.45108 
 2017 17.60834 
 2018 17.59564