# year    value 
 1979  16.6636 
 1980 15.67796 
 1981 15.78857 
 1982  15.8232 
 1983 15.84546 
 1984 15.76718 
 1985 15.49124 
 1986 15.36942 
 1987 16.06944 
 1988 15.74646 
 1989 15.89282 
 1990 15.91343 
 1991 15.90772 
 1992 15.09469 
 1993 15.61798 
 1994 15.60134 
 1995 15.89412 
 1996 15.38768 
 1997 15.25966 
 1998 15.88496 
 1999 16.35805 
 2000 15.41633 
 2001 15.72114 
 2002 15.83703 
 2003 15.89984 
 2004 16.18638 
 2005  16.1001 
 2006 16.34926 
 2007 15.71835 
 2008 16.33093 
 2009 16.31858 
 2010 15.73417 
 2011 15.91626 
 2012 16.25641 
 2013 16.32931 
 2014 16.27025 
 2015 16.11694 
 2016 16.61112 
 2017 16.61771 
 2018 16.67313 
 2019  16.5759