Year	Percent
2003	20.4
2004	19.4
2005	18.5
2006	18.1
2007	18.5
2008	17.9
2009	17.9
2010	18
2011	17.9
2012	18.7
2013	19.5
2014	19.5
2015	19
2016	18.3
2017	17.3
2018	17.2
2019	16.2
2020	18.4
2021	16.4