New approaches to human mobility: using mobile phones for demographic research.

This article explores new methods for gathering and analyzing spatially rich demographic data using mobile phones. It describes a pilot study (the Human Mobility Project) in which volunteers around the world were successfully recruited to share GPS and cellular tower information on their trajectories and respond to dynamic, location-based surveys using an open-source Android application. The pilot study illustrates the great potential of mobile phone methodology for moving spatial measures beyond residential census units and investigating a range of important social phenomena, including the heterogeneity of activity spaces, the dynamic nature of spatial segregation, and the contextual dependence of subjective well-being.

On nonstable and stable population momentum.

This article decomposes total population momentum into two constituent and multiplicative parts: "nonstable" momentum and "stable" momentum. Nonstable momentum depends on deviations between a population's current age distribution and its implied stable age distribution. Stable momentum is a function of deviations between a population's implied stable and stationary age distributions. In general, the factorization of total momentum into the product of nonstable and stable momentum is a very good approximation. The factorization is exact, however, when the current age distribution is stable or when observed fertility is already at replacement. We provide numerical illustrations by calculating nonstable, stable, and total momentum for 176 countries, the world, and its major regions. In short, the article brings together disparate strands of the population momentum literature and shows how the various kinds of momentum fit together into a single unifying framework.

Population momentum across the demographic transition.

Population momentum is the main driver of global population growth today, and this makes an appreciation of momentum critical to understanding contemporary worldwide growth dynamics. This article traces population momentum along with two recently defined measures of momentum decomposed­stable and nonstable momentum­across the demographic transition. We use historical data and population projections from 16 countries to illustrate some previously ignored empirical regularities of the demographic transition in both the developed and the developing world. We also demonstrate the dynamic nature of stable and nonstable momentum, as changes in stable momentum lead to predictable changes in current and future nonstable momentum. These results suggest that momentum, which by definition is measured at a point in time, can also be considered as a process that unfolds over time.