# year    value 
 1979 19.00032 
 1980 18.84933 
 1981 18.76369 
 1982  18.9252 
 1983 18.84313 
 1984 18.83875 
 1985 18.75192 
 1986  18.7074 
 1987 19.30705 
 1988 18.95885 
 1989   18.891 
 1990 19.15515 
 1991 18.89715 
 1992 18.81993 
 1993 19.29534 
 1994 19.36244 
 1995 19.39954 
 1996 19.06298 
 1997 19.67003 
 1998 19.35693 
 1999 18.82336 
 2000 19.11554 
 2001 19.29649 
 2002 19.48977 
 2003   19.534 
 2004  19.5005 
 2005  19.3098 
 2006  19.3991 
 2007 19.50236 
 2008 19.60264 
 2009 19.86025 
 2010 19.59223 
 2011 19.37346 
 2012 19.82667 
 2013 19.56828 
 2014 19.81615 
 2015 20.17076 
 2016 19.88461 
 2017 19.79327 
 2018  19.9468