Year	Percent
1981	20
1986	58
1988	53.2
1994	65
1997	75.3
1998	71.9
2000	74.2
2001	73.9
2002	78.5
2003	75.3
2004	75.7
2005	76.8
2006	75.7
2007	79
2008	79.4
2010	78
2011	77.8
2012	76.3
2013	77.3
2014	75.7
2015	75.7