Year	Percent
1993	20.2
1996	21.1
1997	22.2
1998	22.6
1999	23
2000	22.9
2001	22.6
2002	22.5
2003	21.9
2004	22.1
2005	21.8
2006	21.7
2007	21.2
2008	21
2009	21.2
2010	21.6
2011	21.3
2012	21
2013	21
2014	21
2015	21.5