Year	Percent
1998	14.2
2000	16.4
2001	16.7
2002	16.7
2003	16.8
2004	15.7
2005	16.1
2006	15.1
2007	16.1
2008	16.7
2009	16.7
2010	16.9
2011	17.1
2012	17.3
2013	16.9
2014	17.2
2015	16.8
2016	17.1