Year Number 2004 0.393849045038223 2005 0.340958386659622 2006 0.418964713811874 2007 0.415193498134613 2008 0.4012451171875 2009 0.292359530925751 2010 0.292717128992081 2011 0.296300768852234 2012 0.313169628381729 2013 0.309244394302368 2014 0.305000483989716 2015 0.289382845163345 2016 0.305349111557007 2017 0.280709505081177 2018 0.281422942876816 2019 0.284793734550476 2020 0.26276308298111 2021 0.30851623415947 2022 0.31724950671196