# year    value 
 1979 15.15324 
 1980 15.92837 
 1981 15.68421 
 1982 15.67039 
 1983 15.27687 
 1984 14.80932 
 1985   15.389 
 1986  15.3647 
 1987 15.14176 
 1988 15.26368 
 1989 15.53841 
 1990 15.33706 
 1991 15.58012 
 1992 15.08443 
 1993 15.35009 
 1994 15.50721 
 1995 14.92025 
 1996 15.36587 
 1997 15.45897 
 1998 15.52672 
 1999 15.21103 
 2000 15.05898 
 2001 15.12654 
 2002  15.4616 
 2003 15.49055 
 2004 15.31838 
 2005 15.60025 
 2006 14.99757 
 2007 15.44573 
 2008 15.54518 
 2009   15.854 
 2010 15.65402 
 2011 15.21757 
 2012 15.36921 
 2013 15.79919 
 2014 15.44259 
 2015 15.74016 
 2016 15.55767 
 2017 15.76946 
 2018 16.20375