Year	Percent
1992	56.7
1996	60.8
1999	62.4
2000	62.2
2001	61.2
2002	60.4
2003	58.4
2004	59.9
2005	58.8
2008	59.7
2009	58.9
2010	59.4
2011	58.3
2012	57.4
2013	57.5
2014	57.5
2015	55.9
2016	55.7