Concept, measurement, and data in migration analysis.

Two methods of computing migration rates-one relating moves to population at risk in place of origin and the other using as a denominator the cross-product of population in places of origin and destination-are discussed. It is concluded that the second assumes implicitly that moves originate and terminate as a random population variable.Some difficulties with this particular model are pointed out and the author suggests that other analytical approaches to migration data be sought and in this connection refers to the literature on the mathematical theory of epidemics.