Year	Percent
1984	91.7
1987	92.7
1990	87
1993	86.6
1996	79.8
1998	90.2
1999	80.1
2000	79.9
2001	77.6
2002	65.2
2003	62.7
2004	63
2005	61.3
2006	65.7
2007	58.5
2008	56.6
2009	54.7
2010	48.1
2011	45
2012	43.5
2013	40.7
2014	37.8
2015	33.1
2016	30.9
2017	27.2