| Year | Value | | 2019 | 41.725580703777 | | 2018 | 44.115187092359 | | 2017 | 47.952135672013 | | 2016 | 48.581512684589 | | 2015 | 47.667975429146 | | 2014 | 49.622009484109 | | 2013 | 53.009297560765 | | 2012 | 52.672207957708 | | 2011 | 56.326002479496 | | 2010 | 69.215844085368 | | 2009 | 72.186363609204 | | 2008 | 71.85047588839 |
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