Year	Percent
1996	23.2
2001	22.8
2002	22.5
2003	22.8
2004	22.5
2005	22.5
2006	21.9
2007	22
2008	22.1
2009	22.4
2010	22.3
2011	22.4
2012	22.5
2013	22.4
2014	22.2
2015	22.2