# year    value 
 1980 15.16194 
 1981  15.8272 
 1982 16.70072 
 1983 17.09966 
 1984 15.20565 
 1985 16.01024 
 1986 15.99013 
 1987  15.9932 
 1988 16.41767 
 1989  15.8993 
 1990 16.15232 
 1991 16.66362 
 1992 17.00343 
 1993 16.33198 
 1994 17.90488 
 1995 16.35863 
 1996 16.06678 
 1997 16.26223 
 1998 17.32844 
 1999 16.67961 
 2000 16.91538 
 2001 16.95282 
 2002 17.19983 
 2003 19.78088 
 2004  16.7764 
 2005 16.65838 
 2006 17.11491 
 2007 17.14818 
 2008 17.23708 
 2009 17.51398 
 2010 17.42495 
 2011   17.002 
 2012 18.28909 
 2013  17.5521 
 2014 16.41602 
 2015 18.92756 
 2016 17.44706 
 2017 18.67831 
 2018 18.35418