Year	Percent
1996	27.9
1997	29.9
1998	31.2
1999	29.9
2000	30.3
2001	30
2002	28.2
2003	27.1
2004	26.7
2005	27.6
2006	27.4
2007	28.9
2008	28.6
2009	28.7
2010	30
2011	29.7
2012	29.2
2013	29
2014	28.4
2015	27.8
2016	28.1