| Year | Value | | 2021 | 5.0922444697036 | | 2020 | 4.0757549310525 | | 2019 | 4.7752288859171 | | 2018 | 4.8205541305408 | | 2017 | 4.752958666457 | | 2016 | 4.9176496190949 | | 2015 | 4.9460746284562 | | 2014 | 4.8033275083768 | | 2013 | 5.3112918277563 | | 2012 | 5.1895515487749 | | 2011 | 5.3753594550741 | | 2010 | 5.0634213232773 | | 2009 | 5.2348076777179 | | 2008 | 5.8267613895588 | | 2007 | 7.1543916309766 | | 2006 | 7.9650606253989 | | 2005 | 8.481807951988 | | 2004 | 10.041455550438 | | 2003 | 10.72598415818 | | 2002 | 10.102460353717 | | 2001 | 8.8656387665198 | | 2000 | 9.8403808457015 | | 1999 | 11.015682076898 | | 1998 | 11.7360159923 |
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