Year	Percent
1997	50.82
1998	51.37
1999	52.94
2000	53.98
2001	55.79
2002	53.99
2003	54.05
2004	55.51
2005	56.67
2006	56.6
2007	58.13
2008	61.42
2009	64.17
2010	66.61
2011	66.96
2012	66.12
2013	66.05
2014	66.11
2015	65.86
2016	66.89
2017	67.08