| Year | Value | | 2020 | 4.4261007159218 | | 2019 | 4.108210258201 | | 2018 | 4.3350369267923 | | 2017 | 4.3184729879515 | | 2016 | 4.3538427630462 | | 2015 | 4.4242751348394 | | 2014 | 4.5654227326566 | | 2013 | 4.814438572428 | | 2012 | 4.8353480616924 | | 2011 | 4.9814728472921 | | 2010 | 5.367046237653 | | 2009 | 5.44444215769 | | 2008 | 6.2157615136622 | | 2007 | 6.2306848768817 | | 2006 | 6.6600066600067 |
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