# year    value 
 1980 14.99581 
 1981 15.22663 
 1982 14.77534 
 1983 15.18996 
 1984 14.75569 
 1985  14.7558 
 1986 14.89449 
 1987 15.13056 
 1988 15.25307 
 1989 15.04867 
 1990 15.34502 
 1991 15.19986 
 1992 14.84143 
 1993 15.00105 
 1994 15.13311 
 1995 15.46581 
 1996 15.07402 
 1997 15.28046 
 1998 15.67284 
 1999 15.38568 
 2000 15.24687 
 2001 15.47178 
 2002 15.57693 
 2003 15.60201 
 2004 15.44266 
 2005 15.84695 
 2006 15.71063 
 2007  15.7907 
 2008  15.5861 
 2009 15.60885 
 2010 15.97061 
 2011 15.60767 
 2012 15.75018 
 2013 15.74054 
 2014 15.71323 
 2015 16.03602 
 2016 16.27409 
 2017 16.08698 
 2018 15.86005