# year    value 
 1980 16.94185 
 1981 16.75339 
 1982 17.30581 
 1983 16.68983 
 1984 16.38016 
 1985 17.00362 
 1986  17.3533 
 1987 17.67411 
 1988 16.70467 
 1989 17.13615 
 1990 16.90726 
 1991  17.1722 
 1992 17.05424 
 1993 17.22546 
 1994 17.57808 
 1995 17.33787 
 1996 16.89157 
 1997 17.98031 
 1998 17.79044 
 1999 16.75402 
 2000 16.80679 
 2001 17.28338 
 2002 17.03572 
 2003  17.0714 
 2004 17.24038 
 2005 17.48178 
 2006 17.79976 
 2007 16.26886 
 2008 17.37173 
 2009 17.32576 
 2010 16.94215 
 2011 17.31109 
 2012 17.36091 
 2013 17.08756 
 2014 17.86418 
 2015   18.296 
 2016 17.43084 
 2017 17.86976 
 2018 16.61736