Year	Percent
1970	0.39554
1971	0.40647
1972	0.42573
1975	0.45179
1976	0.43884
1978	0.50757
1979	0.51691
1980	0.49933
1999	0.72537
2000	0.73381
2011	0.88891
2014	0.88247
2015	0.86971