Year	Percent
1971	0.57863
1972	0.64769
1973	0.68227
1977	0.70013
1978	0.80728
1979	0.77081
1980	0.80818
1981	0.8138
1986	0.81419
1988	0.78915
1990	0.77159
1992	0.77136
1993	0.76274
1994	0.76309
1995	0.77777
1996	0.78135
1997	0.78713
1998	0.79753
1999	0.81021
2000	0.81146
2001	0.8167
2002	0.8199
2003	0.82509
2004	0.83256
2005	0.83531
2006	0.84462
2007	0.85335
2008	0.86561
2009	0.8784
2010	0.89026
2011	0.90112
2012	0.91288
2013	0.92259
2014	0.93476
2015	0.94391
2016	0.94597