Year	% of cohort
1971	99.6230621337891
1972	99.6717529296875
1973	99.7434768676758
1974	99.8192291259766
1975	99.7788314819336
1976	99.7206192016602
1977	99.7953720092773
1978	99.8403701782227
1979	99.5629272460938
1980	99.8156509399414
1981	99.8594589233398
1982	99.8438491821289
1983	99.8334732055664
1984	99.8805084228516
1985	99.8345489501953
1986	99.9002304077148
1987	99.9130935668945
1988	99.8648223876953
1989	99.877082824707
1990	99.9170074462891
1991	99.964973449707
1998	99.9749526977539