| Year | Value | | 2014 | 10.83 | | 2013 | 11.05 | | 2012 | 11.27 | | 2011 | 11.25 | | 2010 | 11.45 | | 2009 | 11.07 | | 2008 | 11.12 | | 2007 | 11.23 | | 2006 | 11.18 | | 2005 | 11.13 | | 2004 | 10.71 | | 2003 | 11.34 | | 2002 | 11.94 | | 2001 | 12.58 | | 2000 | 12.61 | | 1999 | 12.6400003433 | | 1998 | 12.4200000763 | | 1997 | 12.3599996567 | | 1996 | 12.2700004578 | | 1995 | 12.3800001144 | | 1994 | 12.4638996124 | | 1993 | 12.4762001038 | | 1992 | 12.6906995773 | | 1991 | 13.20470047 | | 1990 | 13.2264003754 | | 1989 | 13.579500198364 | | 1988 | 13.372900009155 | | 1987 | 13.456299781799 | | 1986 | 13.260499954224 | | 1985 | 13.071299552918 | | 1980 | 12.546099662781 |
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