# year    value 
 1979  16.8201 
 1980 16.40967 
 1981 16.20418 
 1982  16.7086 
 1983 16.01825 
 1984 15.62902 
 1985 16.04529 
 1986 16.46756 
 1987 16.76143 
 1988 16.14188 
 1989 16.52432 
 1990 16.20457 
 1991 16.34293 
 1992 15.89506 
 1993   16.184 
 1994 16.65058 
 1995 16.87622 
 1996 16.30734 
 1997 17.29944 
 1998 17.13189 
 1999  16.1871 
 2000 16.03992 
 2001   16.694 
 2002 16.40885 
 2003 16.77173 
 2004 16.63724 
 2005 17.20194 
 2006  17.5405 
 2007 16.08862 
 2008 17.07119 
 2009 16.88479 
 2010 16.73244 
 2011 16.84508 
 2012  16.9387 
 2013 16.64161 
 2014 17.12837 
 2015 17.72194 
 2016 17.04082 
 2017 17.38175 
 2018 16.20539