Year	Percent
2003	18.9
2004	19.2
2005	19.3
2006	19.5
2007	18.9
2008	18.4
2009	18.7
2010	19.8
2011	19.5
2012	19.3
2013	19.4
2014	19.9
2015	20.6
2016	20.3
2017	20.3
2018	20.1
2019	20
2020	20.1
2021	20.1