| Year | Value | | 2021 | 0.68304078994001 | | 2020 | 0.26741958630751 | | 2019 | 3.7589478004558 | | 2018 | 3.3955234568193 | | 2017 | -6.3961709338078 | | 2016 | 0.94752178783803 | | 2015 | 8.048342794131 | | 2014 | 5.5929821548758 | | 2013 | 3.4337893862308 | | 2012 | -1.8443713270226 | | 2011 | -1.6778971630762 | | 2010 | 2.3088990236029 | | 2009 | -10.880460521629 | | 2008 | 4.1080151857589 | | 1981 | 17.735966921315 |
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