| Year | Value | | 2022 | 20.25844580538 | | 2021 | 21.577344405973 | | 2020 | 20.599632768647 | | 2019 | 18.282362134237 | | 2018 | 18.680721252508 | | 2017 | 15.536197184679 | | 2016 | 16.33080152107 | | 2015 | 16.319960092343 | | 2014 | 13.106107385989 | | 2013 | 13.923862182009 | | 2012 | 10.921567421419 | | 2011 | 10.322583196296 | | 2010 | 13.877874978433 | | 2009 | 14.735835120507 | | 2008 | 9.0031106514397 | | 2007 | 10.016911283015 |
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