Year	Percent
1999	21.2
2001	20.9
2002	20.8
2003	20.8
2004	20.2
2005	20.2
2006	22.1
2007	22.1
2008	22.4
2009	22.4
2010	21.7
2011	22.2
2012	22
2013	22.2
2014	22
2015	21.8
2016	22.8