Year	Percent
1990	31.7
1997	45.4
1999	42.6
2000	47.8
2001	44.2
2002	46.6
2004	43.9
2005	45.3
2006	43.6
2007	41.8
2008	38.5
2009	36.9
2011	33.7
2012	33.7
2013	35.2
2014	36
2015	34.8
2016	32.1