EDITOR,—R W Lacey's letter makes no reference to any scientific paper on the epidemiology of bovine spongiform encephalopathy.1 As a result it contains too many omissions, errors, and misconceptions to pass into the literature unchallenged.

Lacey's description of the cohort study to examine the risk of maternal transmission is incorrect. This study is comparing the incidence of bovine spongiform encephalopathy in offspring of dams that developed clinical signs of the disease and in offspring of dams that reached at least 6 years of age without developing …