How (Not) to Control for Population Size in Ecological Analyses

Abstract

It is common for social scientists to use formal quantitative methods to compare ecological units such as towns, schools, or nations. In many cases, the size of these units in terms of the number of individuals subsumed in each differs substantially. When the variables in question are counts, there is generally some attempt to neutralize differences in size by turning variables into ratios or by controlling for size. But methods that are appropriate in many demographic and epidemiological contexts have been used in settings where they may not be justified and may well introduce spurious relations between variables. We suggest local regressions as a simple diagnostic and generalized additive models as a superior modeling strategy, with double-residualized regressions as a backup for certain cases.