Year	Percent
1989	63.3
1990	61.2
1991	56.7
1992	56.9
1993	58
1994	59.3
1995	59.8
1996	59.6
1997	57.2
1998	60.8
1999	59
2001	58.8
2002	59.4
2003	61.7
2004	61.8
2005	62.9
2006	60.8
2007	60
2008	59.2
2009	55.4
2010	57.1
2011	60.2
2012	59.9
2013	56.7
2014	55.1
2015	54
2016	54.2