| Year | Value | | 2022 | 21.561368738615 | | 2021 | 25.07856534277 | | 2020 | 27.129107081382 | | 2019 | 29.030450378654 | | 2018 | 33.163079237609 | | 2017 | 30.590012549498 | | 2016 | 30.953204024514 | | 2015 | 29.522159536934 | | 2014 | 31.450331780095 | | 2013 | 28.334763591027 | | 2012 | 30.912255614517 | | 2011 | 32.558275819566 |
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