# year    value 
 1980 16.73986 
 1981 16.64328 
 1982 16.61177 
 1983  16.6878 
 1984 16.05778 
 1985 16.45841 
 1986 16.50303 
 1987 16.91281 
 1988 16.96849 
 1989 16.69314 
 1990 16.95701 
 1991 16.71741 
 1992 16.55476 
 1993 16.49739 
 1994 16.90744 
 1995 16.95743 
 1996 16.53271 
 1997 16.92199 
 1998 17.43344 
 1999 17.41866 
 2000 17.07427 
 2001 17.30482 
 2002 17.54243 
 2003 16.99337 
 2004  17.5784 
 2005 17.11073 
 2006  17.6016 
 2007 17.67275 
 2008 17.22116 
 2009 17.53992 
 2010 17.44848 
 2011 16.98101 
 2012 16.72462 
 2013 17.39005 
 2014 17.08767 
 2015 17.56532 
 2016 17.72997 
 2017 17.69404 
 2018 17.41986