| Year | Value | | 2021 | 31.09763348793 | | 2020 | 30.966821262933 | | 2019 | 29.487765835811 | | 2018 | 29.533501029042 | | 2017 | 29.670706608735 | | 2016 | 29.705008003659 | | 2015 | 29.624971415504 | | 2014 | 29.793048250629 | | 2013 | 29.616967756689 | | 2012 | 29.294534644409 | | 2011 | 30.179510633432 | | 2010 | 30.348730848388 | | 2009 | 29.884518637091 | | 2008 | 30.419620397896 | | 2007 | 29.919963411845 | | 2006 | 29.678710267551 |
|