# year    value 
 1980 17.43102 
 1981 16.10292 
 1982 16.90837 
 1983 17.13499 
 1984   16.533 
 1985 16.38808 
 1986  16.5564 
 1987 16.78516 
 1988  17.3487 
 1989 17.00763 
 1990 17.52651 
 1991  16.9601 
 1992 16.37935 
 1993 16.44514 
 1994 17.10175 
 1995 17.45631 
 1996 16.68775 
 1997 16.72734 
 1998 17.94149 
 1999 17.56322 
 2000 16.64663 
 2001 17.68698 
 2002 17.29709 
 2003 17.27917 
 2004 17.45448 
 2005 17.80905 
 2006 18.20916 
 2007 17.50042 
 2008 17.77808 
 2009 17.26762 
 2010 17.89367 
 2011 17.48005 
 2012 16.85178 
 2013 17.67874 
 2014 17.53065 
 2015 17.54436 
 2016 17.19719 
 2017 17.73905 
 2018  17.1247