A Comparative Study of ‘Contemporaneous’ and ‘Traditional’ Data Sets
What is the ambient population and why does it matter?
The term ‘ambient population’ refers to the actual number of persons who are present within a particular area at any given time. Population counts have traditionally been derived from decennial censuses but these have tended to be limited in their ability to capture daily fluctuations in population size that can occur when people move between different activity types and locations. For example, ONS (2013, p. 1) note that the City of London typically experiences a 56 fold increase from usually resident to workday population! Since reliable population figures are fundamental to the efficient allocation of public resources and service provision, there is growing interest in the use of alternative data sources as enumerators of the population.
The ambient population in the context of crime
Accurate representations of the ambient population are extremely relevant for the field of crime analysis because they can facilitate the identification of areas where the risk of victimisation is comparatively high, or low, relative to the size of the underlying population. To illustrate, a UK city centre people-based offence rate based on a ‘traditional’ denominator, such as a usually resident population count, is likely to overstate the risk of victimisation because these areas tend to be less densely populated i.e. there might appear to be more crime per head of population than is actually the case. An ambient population figure is likely to generate a more representative crime rate because it includes additional constructs of the population (e.g. workers and visitors) and also because it can be aligned more closely with the timing of offences.
Emily Sheard, Nick Malleson, and Mark Birkin