# year    value 
 1980 18.43127 
 1981 19.13873 
 1982 20.14255 
 1983 20.71391 
 1984 18.63938 
 1985 19.28028 
 1986 19.44203 
 1987 19.18295 
 1988 19.81586 
 1989 19.48699 
 1990 19.85546 
 1991 20.19398 
 1992 20.77449 
 1993 19.86338 
 1994 21.40568 
 1995 20.09427 
 1996 19.51691 
 1997  19.8365 
 1998 20.62231 
 1999 20.18815 
 2000 20.44328 
 2001 20.34193 
 2002 20.72507 
 2003 22.34513 
 2004 20.09783 
 2005 20.06908 
 2006 20.63401 
 2007 20.61708 
 2008 20.61823 
 2009 20.86326 
 2010 20.80093 
 2011 20.40944 
 2012 21.53572 
 2013 21.14622 
 2014 20.07014 
 2015 22.30173 
 2016 20.88978 
 2017  22.0713 
 2018 22.08991