Year	Percent
1987	38.4
1994	42.5
1998	37.9
1999	47.9
2000	45.9
2003	41.9
2004	42.4
2005	41.2
2006	41.1
2007	42
2008	38.1
2009	37.1
2010	37.5
2011	34.1
2012	34.6
2013	35.7
2014	34.4
2015	34.9
2016	34.3