Year	% of cohort
1971	99.6971435546875
1972	99.7133712768555
1973	99.8057174682617
1974	99.845947265625
1975	99.8193206787109
1976	99.7621688842773
1977	99.822998046875
1978	99.9110870361328
1979	99.6310272216797
1980	99.8634796142578
1981	99.9221267700195
1982	99.8609313964844
1983	99.8886184692383
1984	99.9218597412109
1985	99.8639831542969
1986	99.9271011352539
1987	99.9578628540039
1988	99.8852233886719
1989	99.9100036621094
1990	99.9479675292969
1991	99.9879302978516
1998	99.9914398193359