In the mid 1970s, approximately three quarters of
the original cohort (n=35 104) were “flagged” at
National Health Service central registries in Scotland
and England, so that subsequent cancers and deaths
would be reported to the study, even if the woman
was no longer under general practice follow-up. The
remaining 24% of women could not be flagged because
they, or their general practitioner, left the study before
flagging took place.