Sampling Development

Research in developmental psychology requires sampling at different time points. Accurate depictions of developmental change provide a foundation for further empirical studies and theories about developmental mechanisms. However, overreliance on widely spaced sampling intervals in cross-sectional and longitudinal designs threatens the validity of the enterprise. This article addresses how to sample development to accurately discern the shape of developmental change. The ideal solution is daunting: to summarize behavior over 24-hour intervals and collect daily samples during the critical periods of change. The article also addresses the magnitude of errors due to undersampling and the risks associated with oversampling. When daily sampling is not feasible, suggestions are offered for sampling methods that can provide preliminary reference points and provisional sketches of the general shape of a developmental trajectory. Denser sampling then can be applied strategically during periods of enhanced variability, inflections in the rate of developmental change, or in relation to key events or processes that may affect the course of change. Despite the challenges of dense repeated sampling, researchers must take seriously the problem of sampling on a developmental time scale if we are to know the true shape of developmental change.