Year	Percent
1998	21.5
2000	22.1
2001	22.5
2002	22.6
2003	22.5
2004	22.1
2005	21.9
2006	21.7
2007	22.4
2008	22.3
2009	21.9
2010	22
2011	22
2012	21.9
2013	22.1
2014	22
2015	21.5
2016	21.8