Year	% of cohort
1971	99.8023681640625
1972	99.8261489868164
1973	99.8267364501953
1974	99.8480987548828
1975	99.8193206787109
1976	99.8004531860352
1977	99.822998046875
1978	99.9204177856445
1979	99.7126007080078
1980	99.8767395019531
1981	99.9221267700195
1982	99.882926940918
1983	99.8886184692383
1984	99.9278564453125
1985	99.8873062133789
1986	99.9271011352539
1987	99.9578628540039
1988	99.8877563476562
1989	99.9100036621094
1990	99.9479675292969
1991	99.9967193603516
1998	99.9914398193359