Year	Percent
1997	28.52
1998	29.07
1999	27.07
2000	26.78
2001	26.64
2002	27.37
2003	27.24
2004	28.2
2005	29.06
2006	29.57
2007	30.55
2008	30.52
2009	26.85
2010	24.56
2011	24.56
2012	25.08
2013	25.53
2014	24.72
2015	25.07
2016	25.14
2017	25.13