Abstract
Considering a cross-classification table table describes an aspect of social mobility (the relation between origin and destination status) for a population of individuals, this paper shows that the usual indices of mobility (or immobility), which are based upon a comparison of the observed frequencies in the mobility table with the corresponding expected frequencies estimated under the assumption of "perfect mobility", are defective in an important respect. A different index is introduced which is not defective in this respect. The index of persistence introduced here can serve to supplement and extend some of the methods developed in the author's earlier work.