Year | Value | 2021 | 20.614068548585 | 2020 | 23.48856616019 | 2019 | 24.049734928477 | 2018 | 23.598187044393 | 2017 | 24.068038298589 | 2016 | 23.289915058438 | 2015 | 22.355213286846 | 2014 | 21.970141400432 | 2013 | 20.83873843434 | 2012 | 18.552500212661 | 2011 | 19.054740942986 | 2010 | 20.22926705448 | 2009 | 20.004806470748 | 2008 | 21.147843815013 | 2007 | 21.302114467809 |
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