Year	Percent
1998	35.3
2000	24.8
2001	23.9
2002	24
2003	23.3
2004	27.2
2005	26.2
2006	29.4
2007	26.5
2008	25.3
2009	24.6
2010	24.6
2011	23.5
2012	23.1
2013	23.8
2014	22.9
2015	24.8
2016	22.9