The predictions of the HPM have withstood a number of preliminary tests based on the aggregate vital data, but the central question we must answer, in order to determine the adequacy of the model in the present context, is that of absolute mortality levels. The amount of information available on mortality levels in pre-industrial European cities is, as De Vries implies, remarkably meagre. The widespread prevalence of burial surpluses in the aggregate vital data for such populations has often been taken to reflect the effects of elevated mortality levels, but this attribution is not conclusive and other explanations – such as depressed fertility – have also been advanced.

This deficiency in our knowledge is partly due to the inherent difficulty of the topic, in the absence of adequate data on population size and structure, but it is also a paradoxical consequence of the growing methodological refinement of historical demographic research itself. As De Vries points out, the latter has been based on techniques which either lend themselves – like family reconstitution – more readily to the study of villages and small towns than to cities, or else – like aggregative back projection – are pitched at the level of national aggregates.