# year    value 
 1980  16.5449 
 1981 16.43357 
 1982 16.37268 
 1983 16.45467 
 1984 16.25639 
 1985 16.34756 
 1986 16.50377 
 1987 16.49796 
 1988 16.62623 
 1989  16.5118 
 1990 16.74012 
 1991 16.73964 
 1992 16.27983 
 1993   16.384 
 1994 16.91846 
 1995 16.76403 
 1996  16.5238 
 1997 16.85392 
 1998 17.20899 
 1999 16.73542 
 2000 16.88248 
 2001  17.0329 
 2002 17.08803 
 2003 16.99734 
 2004 16.82513 
 2005  17.1039 
 2006 17.19647 
 2007 17.07829 
 2008 17.00303 
 2009 17.03019 
 2010 17.17841 
 2011 17.14697 
 2012 17.18949 
 2013 17.18074 
 2014 17.19028 
 2015 17.41245 
 2016 17.43664 
 2017 17.42516 
 2018 17.32554