RANDOMIZATION IN THE CANADIAN NATIONAL BREAST SCREENING STUDY - A REVIEW FOR EVIDENCE OF SUBVERSION

THE AUTHORS ASSESS THE RANDOMIZATION STRATEGY that had been used in th e Canadian National Breast Screening Study (NBSS). Document experts at a private investigation and security company were hired to assist in reviewing instances in which names of subjects were altered in the ''a llocation books'' (the basic instrument used to assign, at random, par ticipants to either the mammography or the usual-care arm). The review was restricted to records from 3 NBSS centres where women assigned to the mammography arm had a distinctly higher (not necessarily signific ant) number of deaths from breast cancer than those assigned to the us ual-care arm, and to records from 2 centres where, for limited periods , administrative problems were reported. In most cases the underlying, original name could be identified. The document experts found no evid ence of a deliberate attempt to conceal the alterations. A search of t he NBSS database for the underlying and superimposed names revealed th at only 1 of the women whose name had been deleted or superimpsed died of breast cancer. She was in the mammography arm. The authors' thorou gh review of ways in which the randomization could have been subverted failed to uncover credible evidence of it. They conclude that even if there had been acts of subversion, they could only have been few in n umber and, given that there was only 1 death from breast cancer in the group reviewed, the alterations could have had only a trivial effect on the study findings as reported in 1992.