Year | Value | 2021 | 14.061462947107 | 2020 | 13.565824219078 | 2019 | 13.514939767621 | 2018 | 14.047920888311 | 2017 | 13.412129056696 | 2016 | 13.026332190764 | 2015 | 13.782845074185 | 2014 | 15.138083112839 | 2013 | 15.161096289174 | 2012 | 15.323935641709 | 2011 | 15.821007612765 | 2010 | 15.285368875228 | 2009 | 15.10455223023 | 2008 | 16.873885776846 |
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