Year	Percent
1989	48.2
1990	45.5
1991	40.8
1992	41.4
1993	42.8
1994	43.5
1995	43.8
1996	43.7
1997	41.4
1998	44.6
1999	41.9
2001	41.6
2002	42.7
2003	45.1
2004	44.9
2005	46.1
2006	44
2007	43.1
2008	43
2009	38.4
2010	40.2
2011	44.3
2012	44.1
2013	40.2
2014	38.1
2015	37
2016	36.8