Résonance et équilibres. Alternatives du modèle Samuelson-Easterlin

[fre] simples et générales, mais tout comme celui de Samuelson, il est homogène et n'est donc pas soumis à des effets d'échelle. Or, l'opposition éventuelle n'est pas entre modèles linéaires et non linéaires, mais entre modèles homogènes et inhomogènes. Un exemple de ces derniers est fourni» Non seulement, il décrit une situa­tion ancienne bien connue (autorégulation des populations paysannes au xvnie siècle), mais il présente des particularités analogues à celles que recherchait Samuelson (fécondité variable selon l'effectif, fluctuations amorties ou explosives selon les paramètres). [eng] Fluctuation and stability. Hervé Le Bras. P. Samuelson has formalised Easterlin's model in such a way as to rediscover the Cobweb model. He therefore concluded on conditions of instability. It is shown that it suffices to change the definition of age groups or their number in order to obtain the opposite effect. Another formalisation ist therefore suggested which permits the separation of a component of convergency of stable populations from a component of fluctuations in the fertility rates. This new model comprises simple and general properties : like Samuelson s model, it is homogeneous and is not therefore subject to scale effects. Now the main opposition is not between linear and non linear models, but between homogeneous and inhomogeneous models. An example of the latter is provided. Not only does it describe an old, well-known situation (self-regulation of rural populations in the 18th century), but it also displays certain characteristics analogous to those sought by Samuelson (fertility varying according to numbers, subdued or explosive fluctuations according to the parameters).