| Year | Value | | 2022 | 18.633294748395 | | 2021 | 22.70320408357 | | 2020 | 17.548113863038 | | 2019 | 24.761604677078 | | 2018 | 25.552836551435 | | 2017 | 25.590905229065 | | 2016 | 28.053343467751 | | 2015 | 28.52108584369 | | 2014 | 26.609127009685 | | 2013 | 29.205896652189 | | 2012 | 29.068733282477 | | 2011 | 34.072044515806 | | 2010 | 34.611863074843 | | 2009 | 33.337933532392 | | 2008 | 37.321852963908 | | 2007 | 36.91022607904 |
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