| Year | Value | | 2021 | 11.381598621887 | | 2020 | 11.841996423859 | | 2019 | 12.003989610935 | | 2018 | 12.173878249451 | | 2017 | 12.184301943268 | | 2016 | 10.638963161967 | | 2015 | 10.536581779781 | | 2014 | 10.949109255438 | | 2013 | 9.7087435618013 | | 2012 | 9.3157151424039 | | 2011 | 10.617706978392 | | 2010 | 10.563465020975 | | 2009 | 9.9401842671795 |
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