Analysis of the bovine spongiform encephalopathy maternal cohort study, revisited

The bovine spongiform encephalopathy (BSE) maternal cohort study provided r obust evidence of an enhanced risk of developing BSE for offspring of BSE-a ffected dams. We present for the first time, but in retrospect, an interim analysis of the BSE maternal cohort study and set it in historical context, some of which has only been revealed through the BSE inquiry. We also cons ider the implications for design of extending the BSE maternal cohort study once an enhanced risk to exposed calves had been established, to assess th e risk to calves born further from the clinical onset of BSE in the dam tha n those in the original study. We demonstrate that, if a data monitoring co mmittee had been established, conclusions similar to those based on the fin al results could have been drawn several years before the completion of the BSE maternal cohort study. Further, we conclude that an extension of the c ohort study is unlikely to have been commissioned because of the substantia l financial investment required, yet low power, and practical difficulties associated with implementation of any worthwhile extension.