| Year | Value | | 2021 | 14.014059387214 | | 2020 | 13.124681517238 | | 2019 | 13.477166405272 | | 2018 | 13.51707016464 | | 2017 | 13.397586249336 | | 2016 | 13.725599710157 | | 2015 | 13.670199724712 | | 2014 | 13.146390127154 | | 2013 | 13.227739684855 | | 2012 | 13.235354295499 | | 2011 | 13.547864485235 | | 2010 | 13.057981501804 |
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