Year	Percent
1989	51.7
1991	60.1
1995	50.9
1996	52.6
1998	52.2
1999	49.9
2000	44.6
2001	46.2
2002	46.5
2003	47.2
2004	45
2005	45.1
2006	42.4
2007	39.2
2008	43.4
2009	42.2
2010	41.3
2011	41.3
2012	38.9
2013	35
2014	34.9
2015	31.8
2016	30.7