# year    value 
 1980 15.14118 
 1981 14.97741 
 1982 15.03794 
 1983 14.93604 
 1984 14.40847 
 1985 14.99182 
 1986 14.75069 
 1987 14.87036 
 1988  14.8839 
 1989 15.05395 
 1990 14.95958 
 1991 14.86324 
 1992 14.32359 
 1993 14.78217 
 1994 14.97837 
 1995   14.628 
 1996  14.7845 
 1997 14.99985 
 1998 15.06376 
 1999 14.99553 
 2000 14.70144 
 2001 14.92175 
 2002 14.90148 
 2003 15.03701 
 2004 15.09137 
 2005 15.08191 
 2006 15.13221 
 2007 14.95325 
 2008 15.14942 
 2009 15.28476 
 2010  14.9299 
 2011 15.03944 
 2012 15.11973 
 2013 15.45123 
 2014 15.37882 
 2015 15.30937 
 2016 15.12534 
 2017 15.46685 
 2018 15.44756