Year Number 2008 0.660762906074524 2009 0.664816915988922 2010 0.376329958438873 2011 0.345713257789612 2012 0.353697180747986 2013 0.330618232488632 2014 0.218982502818108 2015 0.223781511187553 2016 0.228173807263374 2017 0.237186849117279 2018 0.234690293669701 2019 0.250075668096542 2020 0.247393816709518 2021 0.24306446313858 2022 0.240944445133209