Year	Percent
1999	29.6
2001	29.1
2002	29
2003	28.2
2004	31.7
2005	30.8
2006	24.5
2007	25.1
2008	23.7
2009	22.9
2010	25
2011	24
2012	24.5
2013	24.7
2014	25.7
2015	26.7
2016	25.3