Defining and Identifying Only Children: A Research Note on the Concept and Measurement Illustrated With UK Survey Data.

Despite increasing interest in the circumstances and outcomes of only children in the demographic literature, the conceptualization of this group has received limited scholarly attention. This research note argues for greater engagement by demographers and social scientists in the conceptualization and identification of only children by addressing three aims. First, we outline potential definitions of only children, present a framework to guide researchers' decisions, and evaluate whether only children can be reliably identified using the British birth cohort studies. Second, we show that the prevalence estimates are contingent on the timing of measurement in childhood, indicating the need for caution when deriving only-child status from cross-sectional household grid data. Third, we demonstrate that both the size and the characteristics of the only-child group may differ across definitions, highlighting that the accurate operationalization of some definitions is particularly restricted by survey designs that prioritize mothers for data collection on children and families. We argue that researchers interested in sole children's outcomes must choose the most appropriate measure for a given research question and, given that many datasets limit how accurately any indicator of only children can capture the chosen definition, reflect on how the operationalization of their measure might affect the results.