Year	Percent
1987	19
1989	21.6
1993	24.2
2004	24.2
2005	28
2006	22.8
2007	22.3
2008	22
2009	21.5
2010	23.1
2011	23.1
2012	23.9
2013	24.4
2014	24
2015	23.8