Hypertension and cerebral infarction.

At the time when this estimate was made a total of 4,263 children (all in Grade O, I, or II initially) had been admitted to the unvac cinated group. According to the estimate 98 cases of leprosy would be expected to develop among them during a period of follow-up of five years. It was not known whether the population of child contacts was stationary, but it was suspected that, as a result of the treatment of known cases, the risk of contracting leprosy might be falling. In addition it was uncertain how effectively the participants could be traced for follow-up examinations, and whether it would be possible to continue these for as long as five years. In the circumstances it was safer to assume that perhaps only about half of the above total of 98 cases would develop and be detected in the course of the trial. If, say, 50 cases were found in the unvaccinated group, then it would not be permissible to claim a clear benefit from B.C.G. vaccination unless 25 or fewer cases were found in a randomly allocated vaccinated group of equal size (any lesser difference could be attributed to chance). Since it was important to be able to detect a reduction in leprosy incidence due to B.C.G. vaccination, if it occurred, which was less than 50%, it was decided to increase the number of participants in the trial, and the intake was continued.