# year    value 
 1980 14.88361 
 1981 15.09577 
 1982 14.59838 
 1983 14.84584 
 1984 14.77148 
 1985 14.75946 
 1986 15.02269 
 1987 14.76031 
 1988 15.19243 
 1989 14.91615 
 1990 15.52095 
 1991 15.15688 
 1992 14.87522 
 1993 15.03485 
 1994 15.13605 
 1995 15.20686 
 1996 14.78522 
 1997 15.03827 
 1998   15.561 
 1999 15.11194 
 2000 15.47516 
 2001 15.48335 
 2002 15.43715 
 2003   15.343 
 2004 15.32082 
 2005 15.69366 
 2006  15.4045 
 2007 15.71187 
 2008 15.47834 
 2009 15.32508 
 2010 15.95116 
 2011 15.44108 
 2012 15.69611 
 2013 15.36968 
 2014 15.65182 
 2015   15.684 
 2016 16.23975 
 2017 15.81345 
 2018 15.56737