"Methods based on survival probabilities are often used for estimating net migration by age over a given period, and the bias introduced by these methods [has] been discussed by many authors.  This note shows that the results obtained in this respect by Wunsch and Termote (and used by Courgeau as well) under the hypothesis of an even distribution of migrants over the period, are actually valid for another assumption." (SUMMARY IN ENG AND SPA)