| Year | Value | | 2021 | 5.4734585802547 | | 2020 | 5.8519132800461 | | 2019 | 4.5292271404841 | | 2018 | 4.5556224781013 | | 2017 | 5.2995190511802 | | 2016 | 5.6758842977101 | | 2015 | 4.702895031847 | | 2014 | 4.9529249197468 | | 2013 | 5.1540725189032 | | 2012 | 7.6232499719175 | | 2011 | 16.228253093998 | | 2010 | 7.2653969691248 | | 2004 | 4.4831109001119 | | 2003 | 5.0359365427949 | | 2002 | 5.1203065753378 | | 2001 | 5.6715524231814 | | 2000 | 4.7396517189893 | | 1999 | 4.4448143832196 | | 1998 | 5.3425394264383 | | 1997 | 4.7351355161597 |
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