# year    value 
 1979  13.9907 
 1980 14.06986 
 1981 14.00777 
 1982  13.7276 
 1983 14.32951 
 1984 13.71444 
 1985 13.77885 
 1986 13.72498 
 1987 14.08427 
 1988 14.25307 
 1989 14.06031 
 1990 14.32379 
 1991 14.18991 
 1992 13.56653 
 1993 13.78634 
 1994  14.4055 
 1995 14.49581 
 1996 13.99057 
 1997 14.43579 
 1998 14.43609 
 1999 14.34123 
 2000 13.98972 
 2001 14.61252 
 2002 14.54721 
 2003 14.72752 
 2004 14.73494 
 2005 15.06039 
 2006 14.83632 
 2007 14.82837 
 2008  14.8707 
 2009 14.83342 
 2010 15.05551 
 2011 14.75691 
 2012 14.96684 
 2013 14.90631 
 2014 14.76885 
 2015 15.25166 
 2016 15.03652 
 2017 15.03381 
 2018 14.93258