Problems and solutions in longitudinal and experimental treatment studies of child psychopathology and delinquency.

This article identifies questions in child psychopathology and delinquency that can best be answered by using longitudinal data and discusses the advantages and problems of longitudinal studies. The article also reviews methodological issues arising in longitudinal research on child psychopathology and proposes solutions to problems. Retrospective and prospective designs are contrasted with the accelerated longitudinal design. It is concluded that more longitudinal studies of child psychopathology including experimental treatment interventions are needed, with repeated data collection from a variety of sources and several years of data before and after the interventions. Such studies, in addition to the traditional longitudinal studies, are likely to improve the understanding of child psychopathology and of factors that influence and reduce serious outcomes for children and adolescents.