# year    value 
 1979 21.65931 
 1980 21.58603 
 1981 21.36045 
 1982 21.31655 
 1983  22.1089 
 1984  21.2765 
 1985 20.93191 
 1986 21.26938 
 1987 21.68985 
 1988 21.54119 
 1989 21.54109 
 1990 21.62875 
 1991 21.48949 
 1992 21.41385 
 1993  21.1886 
 1994 21.41838 
 1995 21.79223 
 1996 21.43484 
 1997 21.32945 
 1998 22.23248 
 1999 21.37398 
 2000 21.32869 
 2001 21.51155 
 2002 21.59974 
 2003  21.9404 
 2004 21.70608 
 2005 21.98445 
 2006  21.7286 
 2007 22.06166 
 2008 21.47194 
 2009 21.69795 
 2010 22.19378 
 2011 21.58638 
 2012 21.75467 
 2013 21.93819 
 2014 21.95118 
 2015 21.76794 
 2016 22.74282 
 2017 22.17419 
 2018 21.87056