Year | Value | 2017 | 21.340698993219 | 2016 | 20.634547752511 | 2015 | 19.691216041693 | 2014 | 19.985154946112 | 2013 | 18.594278012256 | 2012 | 18.532847914061 | 2011 | 18.449258172595 | 2010 | 18.956795528299 | 2009 | 17.874978528788 | 2008 | 17.147398944711 | 2007 | 17.409928823516 | 2006 | 16.741148149632 | 2005 | 16.168215360176 | 2004 | 14.918767860719 | 2003 | 14.569598190491 | 2002 | 14.513859551166 | 2001 | 13.958701755043 | 2000 | 13.072272855978 | 1999 | 12.790216936494 | 1998 | 14.647929335258 | 1997 | 14.767796811526 | 1996 | 14.774607446737 | 1995 | 14.243195780431 | 1994 | 15.030932726508 | 1993 | 14.572302061302 | 1992 | 14.89478824151 | 1991 | 15.480632311095 | 1990 | 16.20308030149 |
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