| Year | Value | | 2021 | 7.5100551799233 | | 2020 | 0.23216384988105 | | 2019 | 4.3021336169902 | | 2018 | 4.2121988886576 | | 2017 | 7.1259892938554 | | 2016 | 7.5046935334092 | | 2015 | 7.3495329919493 | | 2014 | 8.4894678895557 | | 2013 | 5.9252249837121 | | 2012 | 10.377220148275 | | 2011 | 4.7840409124017 | | 2010 | 8.5778775186648 | | 2009 | 12.915395229653 | | 2008 | 6.3898751447311 | | 2007 | 15.288755353982 | | 2006 | 14.341270156006 | | 2005 | 12.737367687726 | | 2004 | 10.79285272157 | | 2003 | 11.872719214035 | | 2002 | 12.03957963054 | | 2001 | 11.28706595409 | | 2000 | 9.0853357185238 | | 1999 | 8.5420790474012 | | 1998 | 8.3414453553891 | | 1997 | 9.4597901612201 | | 1996 | 12.643310401988 |
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