Year	Percent
1990	30.7
1995	46.1
1997	41.4
1999	42.1
2001	43.1
2002	46.2
2003	44.1
2004	42
2005	40.4
2006	42.4
2007	42.5
2008	40.1
2009	38.1
2010	40.5
2011	41.4
2012	36.9
2013	37.3
2014	40.7
2015	36.7
2016	37.3