Year | Value | 2021 | 22.412040581546 | 2020 | 23.715760502438 | 2019 | 18.483046947752 | 2018 | 21.992236936284 | 2017 | 16.930358259566 | 2016 | 16.769425274876 | 2015 | 19.307916061599 | 2014 | 12.646969626692 | 2013 | 10.840639153864 | 2012 | 10.498113846589 | 2011 | 8.8013100722643 | 2010 | 9.5229632513408 |
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