| Year | Value | | 2021 | 3.1285364029492 | | 2020 | 3.1507767402637 | | 2019 | 5.1186718975058 | | 2018 | 5.8747668117862 | | 2017 | 6.0448809551173 | | 2016 | 6.7729454998472 | | 2015 | 7.0384735418733 | | 2014 | 7.4865194633709 | | 2013 | 8.2138707564907 | | 2012 | 7.896000872609 | | 2011 | 7.8786086589555 | | 2010 | 8.2950354842411 | | 2009 | 8.5404496947644 | | 2008 | 9.5137546856286 | | 2007 | 10.02168537311 | | 2006 | 9.2547599302859 | | 2005 | 9.78455570603 | | 2004 | 10.056969236612 | | 2003 | 10.212016411402 | | 2002 | 14.295314900154 | | 2001 | 27.100999873434 | | 2000 | 34.426970646172 | | 1999 | 38.966042341561 | | 1998 | 58.85914266332 | | 1997 | 60.177952963798 |
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