| Year | Value | | 2021 | 22.74775442391 | | 2020 | 21.526702435968 | | 2019 | 26.682859839476 | | 2018 | 21.19263712955 | | 2017 | 22.112084946355 | | 2016 | 20.076762211619 | | 2015 | 20.006484520645 | | 2014 | 23.965383876841 | | 2013 | 21.540652142578 | | 2012 | 18.628777832898 | | 2011 | 16.799529512716 | | 2010 | 14.346610030951 |
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