| Year | Value | | 2022 | 3.9736326574685 | | 2021 | 4.8567837178823 | | 2020 | 4.7186289971932 | | 2019 | 4.2204737110273 | | 2018 | 4.1556666986154 | | 2017 | 3.6032868207991 | | 2016 | 3.6424031775788 | | 2015 | 4.7564672529354 | | 2014 | 4.6962055938867 | | 2013 | 4.8907089163575 | | 2012 | 4.497413295746 | | 2011 | 4.0943558514086 | | 2010 | 3.7996179133745 |
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