# year    value 
 1979 15.81562 
 1980 15.34334 
 1981  15.4715 
 1982 15.36337 
 1983 14.56002 
 1984 14.79812 
 1985 15.32696 
 1986 15.23426 
 1987 15.58542 
 1988 15.90286 
 1989 15.05608 
 1990 15.42785 
 1991 15.76479 
 1992 14.80228 
 1993 15.25717 
 1994 15.93315 
 1995 15.60411 
 1996 15.53609 
 1997 15.41101 
 1998 15.82115 
 1999  16.4002 
 2000 15.35042 
 2001 15.80639 
 2002 16.06733 
 2003 16.13915 
 2004 15.74889 
 2005 15.83174 
 2006 16.45302 
 2007 15.83052 
 2008 15.48017 
 2009 16.50179 
 2010 16.49063 
 2011 15.73052 
 2012 15.59898 
 2013 16.36596 
 2014 15.75898 
 2015 16.06886 
 2016  16.2611 
 2017 16.77399 
 2018 16.34624 
 2019 16.30115