Year Number 1996 0.179107308387756 1998 0.24693064391613 2000 0.266331732273102 2002 0.234331488609314 2003 0.253106504678726 2004 0.262454003095627 2005 0.237393975257874 2006 0.318718701601028 2007 0.329242497682571 2008 0.331731259822845 2009 0.323029518127441 2010 0.304017275571823 2011 0.3041110932827 2012 0.290130853652954 2013 0.235853806138039 2014 0.287785947322845 2015 0.263141095638275 2016 0.264725565910339 2017 0.28424671292305 2018 0.259235680103302 2019 0.264851450920105 2020 0.271182328462601 2021 0.269787937402725 2022 0.266981363296509