Year	Percent
2007	13.5
2008	14.4
2009	14.8
2010	15.4
2011	15.2
2012	16
2013	15.6
2014	16.3
2015	16.2
2016	15.8
2017	16.4
2018	17.1
2019	16.1
2020	15.7
2021	16