| Year | Value | | 2021 | 4.0159136533586 | | 2020 | 4.0159136533586 | | 2019 | 3.6882874671086 | | 2018 | 3.6462162545445 | | 2017 | 3.4655044572097 | | 2016 | 3.4540394033998 | | 2015 | 3.4542579327533 | | 2014 | 3.3942119155155 | | 2013 | 3.7848226195244 | | 2012 | 5.0622186613776 | | 2011 | 5.6376994873029 | | 2010 | 6.7347328349102 | | 2009 | 7.8679759924189 | | 2008 | 10.532771402829 | | 2007 | 10.674366426389 |
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