# year    value 
 1979 21.29509 
 1980 21.41594 
 1981 21.18434 
 1982 21.43146 
 1983 21.48221 
 1984 21.21894 
 1985 21.08861 
 1986 21.28728 
 1987 21.70812 
 1988 21.57808 
 1989 21.17581 
 1990 21.41569 
 1991 21.59186 
 1992 21.36734 
 1993 21.49082 
 1994 21.25834 
 1995 21.87122 
 1996 21.62314 
 1997 21.70335 
 1998 22.12626 
 1999 21.61289 
 2000 21.30528 
 2001 21.61843 
 2002 21.81566 
 2003 21.76042 
 2004 21.53578 
 2005 22.08605 
 2006 21.79085 
 2007 21.49401 
 2008 21.69048 
 2009 21.92669 
 2010  21.8954 
 2011 21.65428 
 2012 21.65135 
 2013 22.00811 
 2014  21.9432 
 2015 22.32498 
 2016  22.2171 
 2017  22.3429 
 2018 21.86553