Year	Percent
1992	47
1996	55.2
1999	58.3
2000	53.7
2001	60.5
2002	53.2
2003	50.9
2004	50.8
2005	46.7
2008	42.6
2009	41.3
2010	38.4
2011	35.1
2012	34.2
2013	32.1
2014	29.8
2015	28.7
2016	28.5