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What we can and cannot say about long‐term longitudinal studies of childhood disorder

Probably the most important message that we can take home from longitudinal findings on the farreaching consequences of childhood disorder is that early pathologic features donot simply go away.For thatmatter,negative fallout fromharmful childhood experiences also does not merely fade with time. Albeit symptom characteristics may undergo change, recognition that adult psychiatric disorder likely isfirstmanifestedorhas itsorigins inchildhood is growing steadily stronger (1–4). Moreover, evidence that childhood disorder may portend a broad range of adverse consequences in adulthood that extendbeyond the realmofpsychopathology suchas elevated risk for cardiovascular disease and other medical conditions (5, 6), early mortality (7), and adult role impairment (8), also is increasing. Clearly, we owe a debt to those researchers who had the forethought and resourcefulness to undertake such long-term studies to elucidate the persistent and pervasive hold that childhood problems may have over the lifespan. Indeed, given thehost ofdifficulties inherent in multiple-wave longitudinal studies including potential selective attrition, declining retention rates, ongoing choices of state-of-the-art measures vs. repeated but outdatedmeasures used in earlier waves, and, not the least among them, covering funding gaps, some may consider it wiser (and certainly less stressful) to avoid them! In this issue of the Acta Psychiatrica Scandinavica, Reef et al. (9) report long-term findings from the Zuid-Holland population-based study of emotional and behavioral problems in children that began in 1983: A range of externalizing and internalizing syndromes assessed when the children were 4–16 years old by parent report were associated significantly with comparable self-reported problems nearly a quarter of a century later, when the sample was between ages 28 and 40. Both homotypic continuity (increased risk for the same syndrome in adulthood) and heterotypic continuity (increased risk for differing syndromes in adulthood) were found, indicating the substantial complexity that characterizes the development, manifestation, and course of early pathologic features into the middle adult years. Those findings contribute to the increasing evidence of continuity of childhood psychopathology, and to our growing knowledge that childhood psychopathology may take many different forms when considered over lengthy periods of time and at later stages of development. Nevertheless, as with all brief instrument studies of psychiatric syndromes, these findings also should be considered introductory in establishing important issues that need to be addressed with more detailed data. The Zuid-Holland Study is among a select group of long-term longitudinal studies that have maintained and followed a large population-based sample of children into the middle adult years. Typically initiated to estimate prevalence of childhood psychopathology and corresponding need for services, or to identify early risks and protective factors, or both, these studies now are examining the course of childhood disorder beyond late adolescence ⁄ early adulthood into more mature life stages, and the alternative forms such disorder may take as samples age. Moreover, they also provide an important repository of data that lends itself to even further broadening of original study goals by adding molecular genetic components and other biological measures to their protocols. Longitudinal studies, especially those with early life information, provide an optimal frame for the investigation of specific gene–environment interaction effects on a range of disorders and other problems. Such studies also have the potential to integrate models of genetic and early environmental risk and protective factors. As any good student of psychology knows, to study what is deviant, one first must be thoroughly familiar with what is considered to be normal. Longitudinal studies of population-based samples can easily speak to what is normative with regard to observed pathologic features as such samples are comprised of natural controls. In addition, repeated assessments of disorder conducted over multiple Acta Psychiatr Scand 2009: 120: 165–166 All rights reserved DOI: 10.1111/j.1600-0447.2009.01420.x 2009 John Wiley & Sons A/S