the minimuln requirements approach was published in the April issue of Economic Geography.1 Richard T. Pratt, the author, makes some thoughtful points comparing an older short-cut method, the location quotient, with the minimum for disaggregated measures. This, in turn, has prompted us to make some further comparisons. We are grateful to him for providing this challenge. Unfortunately, he also demonstrates a lack of under-
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Edward L. Ullman (1968) studied this question.