Year	Percent
2000	37.9
2005	36.6
2006	38.3
2007	36.5
2008	33.8
2009	33.4
2010	29.8
2011	27.6
2012	26.5
2013	25.8
2014	25.6
2015	23
2016	22.1
2017	20.7
2018	21.4
2019	21.5