# year    value 
 1980 14.99435 
 1981 15.16654 
 1982 14.65791 
 1983 14.93834 
 1984  14.8314 
 1985 14.78406 
 1986 15.06149 
 1987  14.8885 
 1988 15.25385 
 1989 14.94784 
 1990 15.57801 
 1991  15.1784 
 1992 14.86522 
 1993 15.05451 
 1994 15.19087 
 1995 15.31799 
 1996 14.93773 
 1997 15.09458 
 1998  15.7118 
 1999  15.1574 
 2000 15.48581 
 2001 15.47162 
 2002 15.47418 
 2003  15.4164 
 2004  15.3204 
 2005 15.82113 
 2006 15.48829 
 2007 15.78556 
 2008 15.59238 
 2009 15.39417 
 2010 16.14664 
 2011 15.47495 
 2012 15.81479 
 2013 15.58386 
 2014 15.80046 
 2015 15.83685 
 2016 16.48755 
 2017 16.05468 
 2018 15.75772