Year	Percent
1970	0.63313
1971	0.63368
1972	0.63654
1973	0.65285
1974	0.67244
1975	0.70804
1976	0.74826
1977	0.7815
1978	0.82672
1979	0.85429
1981	0.90011
1982	0.92274
1983	0.95107
1985	0.97965
1986	0.9878
1987	0.98026
1988	0.97784
1989	0.97238
1991	0.96596
1992	0.95753
1993	0.96039
1994	0.96814
1995	0.97106
1996	0.97609
1997	0.97873
2010	0.95833
2012	0.97859
2013	0.99641