Year	Percent
1999	52.5
2001	55.6
2002	52.3
2003	48
2004	36.3
2005	26.9
2006	22.5
2007	18.7
2008	13.6
2009	19.2
2010	20.5
2011	18.8
2012	17.1
2013	16.2
2014	16.4
2015	13.5
2016	14.1