# year    value 
 1979 16.37961 
 1980 16.60568 
 1981 16.46383 
 1982 16.35983 
 1983 16.40365 
 1984  16.2397 
 1985 16.32767 
 1986 16.46548 
 1987 16.51514 
 1988 16.72258 
 1989  16.5414 
 1990 16.79994 
 1991 16.76941 
 1992 16.20089 
 1993 16.43332 
 1994 17.01327 
 1995 16.81014 
 1996 16.51314 
 1997 16.81746 
 1998 17.28108 
 1999 16.77084 
 2000 16.88896 
 2001   17.109 
 2002 17.16012 
 2003 17.06188 
 2004 16.84786 
 2005 17.18436 
 2006 17.28308 
 2007 17.21296 
 2008 17.12251 
 2009 17.08753 
 2010 17.37625 
 2011 17.20206 
 2012 17.36471 
 2013 17.34561 
 2014 17.31707 
 2015 17.54566 
 2016 17.65914 
 2017 17.64922 
 2018  17.5504