| Year | Value | | 2021 | 6.3822519873015 | | 2020 | 6.9151095890384 | | 2019 | 6.1306444477868 | | 2018 | 6.3082207240149 | | 2017 | 5.5674972526973 | | 2014 | 5.3368656292194 | | 2013 | 5.2936522435043 | | 2012 | 4.8932870480067 | | 2011 | 5.5594494333995 | | 2010 | 4.9573556058098 | | 2009 | 5.9652348210593 | | 2008 | 5.6763622901792 | | 2007 | 5.6958897402092 | | 2006 | 5.9828515972792 | | 2005 | 6.8611993132791 | | 2004 | 6.3278752824337 | | 2003 | 6.461454682438 | | 2002 | 6.6866288007064 | | 2001 | 6.1117098933702 | | 2000 | 5.3562449329286 | | 1999 | 6.0176000777981 | | 1998 | 5.7308895798648 | | 1997 | 5.3080581887482 | | 1996 | 5.1077136301577 | | 1994 | 5.0930009391357 |
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