NBSS: changes were made, suspicious changes were not

In the editorial "The review of randomization in the Canadian National Breast Screening Study: Is the debate over?" (Can Med Assoc J 1997;156:207-9), Dr. Norman F. Boyd writes, "The absence of name alterations had previously been cited by the NBSS investigators as evidence that randomization had not been subverted." He cites 2 articles from the National Breast Screening Study (NBSS). In the context of a review that has documented several instances of name alterations (the majority explicable), his statement, if true, would reflect poorly on NBSS investigators. In fact, Boyd appears to have misunderstood information from the references and, in the process, undermined the credibility of NBSS investigators. NBSS investigators have never reported that name alterations did not occur among the entries for the 90 000 NBSS participants; alterations clearly did occur. We have reported that no suspicious changes in the random allocation sheets had been identified in the participants who died of breast cancer. The external review found that, of 97 unexplained alterations on lines allocating women to mammography, only 1 was associated with a woman who died of breast cancer, and breast cancer had not been diagnosed at the first screen in this case. This alteration was either overlooked by us or detectable only by forensic experts.