On the Use of Pocock and Simon's Method for Balancing Treatment Numbers over Prognostic Factors in the Controlled Clinical Trial

Abstract

One apparent drawback to the use of the method of Pocock and Simon [1975] for sequential assignment in controlled clinical trials, where it is desired to balance treatment numbers for each level of various prognostic factors, is the large amount of calculation required before a new patient entering the trial can be assigned to a treatment series. Pocock and Simon's suggestion that a small computer be programmed to perform the calculations is not realistic, given the resources of many institutions, and this therefore limits the flexibility of application of the method. It is possible, however, to introduce a number of simplifications into the method to enable it to be applied quickly using hand calculations. The method becomes particularly easy to apply if a purely deterministic system is used, that is, where the treatment assignment for a new patient is entirely determined by the prognostic details of that patient and the previous assignments, and there is no random element. This is feasible when the clinician submitting a patient does not have the full information necessary for predicting the next treatment assignment, such as is the case with single patient entries in a multi-center trial. In other situations some form of randomization should be introduced, so that the clinician cannot know in advance what the treatment assignment for his next patient will be. The method is more complicated in this case, but it is still practicable to apply it by hand.

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