Year	% of cohort
1971	99.7451629638672
1972	99.7577667236328
1973	99.7765274047852
1974	99.8255462646484
1975	99.7892303466797
1976	99.7557601928711
1977	99.8108520507812
1978	99.8522567749023
1979	99.6460876464844
1980	99.8412017822266
1981	99.8717880249023
1982	99.8618392944336
1983	99.8552398681641
1984	99.8845596313477
1985	99.8578491210938
1986	99.9104995727539
1987	99.9251403808594
1988	99.876350402832
1989	99.8883285522461
1990	99.9221267700195
1991	99.9692611694336
1998	99.9808578491211