Professor Ronald D. Lee

Department of Demography

Dr. Lee is a demographer and economic demographer, working in three quite different but related areas: intergenerational transfers, probabilistic demographic and fiscal forecasts, and the role of intergenerational transfers in the evolution of life histories.

Intergenerational transfers

The modern human life cycle begins with twenty years of economic dependency in childhood, and ends with another twenty or so years of economic dependency in old age, with forty some years in between in which workers produce more than they consume, and reallocate it to members of other age groups for consumption. From an institutional point of view, these reallocations take place both through the family and the public sector, and take the form of credit transactions, or capital accumulation, or transfers. Lee has developed a formal analytic framework for measuring and interpreting these flows. He has studied their patterns in various societies ranging from hunter-gatherer groups to modern industrial societies. With collaborators, he is launching a project to formulate and estimate national transfer accounts for a number of industrial and Third World nations, to study patterns of transfers in the past and projections for the 21st century.

Probabilistic demographic and fiscal forecasts

Long run population projections are widely used for various kinds of economic, social and environmental planning, but they are very uncertain. This line of research has combined statistical time series methods with demographic models to produce stochastic forecasting models for mortality (the Lee-Carter method), fertility, and population size and age distributions. The methods are extended to produce probabilistic forecasts of public expenditures for various programs. The same line of work examines the fiscal consequences of demographic change, such as population aging or immigration.

The role of intergenerational transfers in the evolution of life histories

The classic evolutionary theory of aging explains that the force of natural selection against mutations with bad effects expressed at some particular age declines with the age at which the effect is expressed, because at older ages there is a smaller proportion of life time survival weighted fertility remaining, so survival matters less for reproductive fitness. However, this theory does not explain why in many species including humans there is considerable postreproductive survival, why mortality typically declines from birth to sexual maturity, and how the low fertility characteristic of humans, other primates, and many other species, could have evolved. Lee has developed a formal theory showing that for species that make post-birth investments in their offspring, the age patterns of cumulated intergenerational transfers (e.g. parental investments) shape the force of natural selection more so than reproduction itself as in the classical theory. Lee is continuing to work on these ideas.