# year    value 
 1979 22.13858 
 1980 23.01705 
 1981 22.90072 
 1982 22.52424 
 1983 23.07177 
 1984 22.13924 
 1985   22.471 
 1986  22.3489 
 1987 22.40646 
 1988 22.31077 
 1989 22.00519 
 1990 22.38378 
 1991 22.79978 
 1992 22.76427 
 1993 22.49096 
 1994 22.64135 
 1995 22.41899 
 1996 22.53279 
 1997 22.74938 
 1998 22.80667 
 1999 21.91429 
 2000 22.10622 
 2001 22.36957 
 2002 22.79831 
 2003 22.55218 
 2004 22.38253 
 2005 22.59999 
 2006  22.3007 
 2007 22.27135 
 2008 22.38187 
 2009 23.30434 
 2010 23.03876 
 2011 22.63921 
 2012 22.84421 
 2013 22.79762 
 2014 22.47726 
 2015 23.22005 
 2016 22.73972 
 2017 22.86386 
 2018 23.05761