Year	Percent
1976	72.65
1978	72.25
1996	54.1
1997	54.46
1998	56.79
1999	57.15
2000	59.76
2001	61.98
2002	63.23
2003	63.52
2004	62.6
2005	63.74
2006	63.95
2007	64.67
2008	65.87
2009	68.66
2010	69.1
2011	69.79
2012	70.07
2013	71.82
2014	70.95
2015	71.92
2016	72.06
2017	71