| Year | Value | | 2019 | 5.5293885409934 | | 2018 | 5.838090708874 | | 2017 | 6.4359706049301 | | 2016 | 5.550313978933 | | 2015 | 8.4999817004162 | | 2014 | 9.3844357380451 | | 2013 | 6.6470764233202 | | 2012 | 6.1435264642094 | | 2011 | 6.2648949444415 | | 2010 | 7.9728112509484 | | 2009 | 10.380544108744 | | 2008 | 6.1202560987776 | | 2007 | 5.5033411537461 | | 2006 | 4.434769154054 | | 2005 | 6.0143036786525 | | 2004 | 6.9716742763546 | | 2003 | 7.5065818085013 | | 2002 | 7.4916541735605 | | 2001 | 4.4502313545678 | | 2000 | 2.7436385045483 | | 1999 | 5.0267682880041 |
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