| Year | Value | | 2021 | 6.3743628319144 | | 2020 | 6.7775489868982 | | 2019 | 6.1568951479646 | | 2018 | 6.1865406599356 | | 2017 | 5.5326421252445 | | 2014 | 5.0427996321866 | | 2013 | 4.9862018950924 | | 2012 | 4.7828578768822 | | 2011 | 5.1808759492004 | | 2010 | 4.6651326132042 | | 2009 | 5.6755805128656 | | 2005 | 6.6427999488879 | | 2000 | 5.1972187472209 | | 1994 | 4.8940670659214 |
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