Demography in macroeconomic models; when population matters for economic cycles

The issue of the onset of Malthusian cycles is investigated by means of a demo-economic model incorporating the age structure of the population. It is shown that the delayed recruitment into the labour force is a major source of demo-economic instability, potentially leading to sustained oscillations. We also compare different modelling strategies for age structure, by showing that the results of our general model are borne out by those provided by a simpler model, based on a representation of age structure via time delays, which allows a deeper mathematical analysis. This suggests that simplified delay models may be of great help in understanding the qualitative properties of complex age structure models.