# year    value 
 1980 16.18922 
 1981 15.87625 
 1982 16.38538 
 1983 16.55652 
 1984 16.14391 
 1985 16.11953 
 1986  16.3185 
 1987 16.68739 
 1988 16.21934 
 1989 16.26586 
 1990 16.18204 
 1991 16.42116 
 1992 16.31161 
 1993 16.52226 
 1994 16.42318 
 1995 16.70365 
 1996 16.10965 
 1997 16.81863 
 1998 16.95367 
 1999  16.3501 
 2000 16.30738 
 2001 16.51075 
 2002 16.67057 
 2003 16.47985 
 2004 16.43307 
 2005  16.8419 
 2006 16.81989 
 2007 16.18843 
 2008 16.56144 
 2009 16.63365 
 2010 16.50338 
 2011 16.53851 
 2012 16.66556 
 2013  16.4677 
 2014 16.88171 
 2015 17.10949 
 2016 16.77615 
 2017  16.9866 
 2018 16.46544