Year Number 2004 0.319958239793777 2005 0.203041076660156 2006 0.266264259815216 2007 0.279377818107605 2008 0.231026411056519 2009 0.216449201107025 2010 0.208097830414772 2011 0.211273431777954 2012 0.230768129229546 2013 0.238375931978226 2014 0.285645455121994 2015 0.25964167714119 2016 0.275300115346909 2017 0.27390918135643 2018 0.279756247997284 2019 0.286051064729691 2020 0.311413139104843 2021 0.325010359287262 2022 0.30890029668808