# year    value 
 1979 22.10084 
 1980 23.26734 
 1981 22.61975 
 1982 21.98449 
 1983 23.03211 
 1984 22.78058 
 1985 22.18483 
 1986 22.43751 
 1987 22.27996 
 1988 23.55509 
 1989 22.32145 
 1990 22.80044 
 1991 22.58322 
 1992  20.9625 
 1993 21.39731 
 1994 22.89781 
 1995 22.45988 
 1996 22.58013 
 1997 22.31013 
 1998 22.85457 
 1999  22.2873 
 2000 22.94501 
 2001 23.25673 
 2002 23.16956 
 2003 23.23007 
 2004 21.44818 
 2005 22.86205 
 2006 23.88038 
 2007 23.22715 
 2008 22.65384 
 2009 22.11794 
 2010 23.05352 
 2011 24.04838 
 2012 24.12982 
 2013 23.11976 
 2014 22.45297 
 2015 23.30882 
 2016  23.5291 
 2017 23.29423 
 2018 23.63079