Year	% of cohort
1971	99.6903991699219
1972	99.6926803588867
1973	99.7285766601562
1974	99.8041076660156
1975	99.7605133056641
1976	99.7133026123047
1977	99.7992477416992
1978	99.78759765625
1979	99.5829315185547
1980	99.8074035644531
1981	99.8239135742188
1982	99.8417587280273
1983	99.8234481811523
1984	99.8433609008789
1985	99.8297805786133
1986	99.8946914672852
1987	99.8939895629883
1988	99.8654937744141
1989	99.8676834106445
1990	99.8975296020508
1991	99.9430236816406
1998	99.9708099365234