Year	Percent
1996	55.41
1997	52.43
1998	53.92
1999	56.75
2000	58.32
2001	58.23
2002	58.24
2003	58.68
2004	59.76
2005	61.47
2006	61.12
2007	61.11
2008	62.62
2009	66.89
2010	68.29
2011	68.18
2012	68.12
2013	67.95
2014	68.62
2015	68.39
2016	68.15
2017	69.79