Year Number 1996 0.425513386726379 1998 0.394628912210464 2000 0.328637719154358 2002 0.381930857896805 2003 0.355438649654388 2004 0.347725838422775 2005 0.365848004817963 2006 0.406286180019379 2007 0.38243693113327 2008 0.357337206602097 2009 0.398354142904282 2010 0.411506086587906 2011 0.412089228630066 2012 0.398291945457459 2013 0.386693984270096 2014 0.517064273357391 2015 0.498630166053772 2016 0.51005220413208 2017 0.480442553758621 2018 0.480384886264801 2019 0.491095125675201 2020 0.52329158782959 2021 0.495514720678329 2022 0.458686977624893