| Year | Value | | 2020 | 0.36298431181804 | | 2019 | 0.36886145379365 | | 2018 | 0.4118161278427 | | 2017 | 0.38460133187441 | | 2016 | 0.26326311663942 | | 2015 | 0.26955598252142 | | 2014 | 0.27685608063381 | | 2013 | 0.28485025015421 | | 2012 | 0.29317755979279 | | 2011 | 0.30060505242507 | | 2010 | 0.30854259949456 | | 2009 | 0.31560839916406 | | 2008 | 0.24247597063131 | | 2007 | 0.24804847859466 | | 2006 | 0.25403147958095 | | 2004 | 0.26990771855103 |
|