Epidemiology: A valuable way to study individual differences in risk and resiliency?

This guest post is by Odilia Laceulle. Odilia is finishing her PhD project at the Interdisciplinary Center for Psychiatric Epidemiology (UMC Groningen, with Prof. Ormel). She focuses on the influence of stressful life events on temperament and stress-reactivity during adolescence using data from the large cohort study TRAILS (TRacking Adolescents’ Individual Lifes Survey).

It is no surprise that many children and adolescents we see in clinical practice need help after being exposed to severe stress. However, not all children who are exposed to stress seek clinical help; some are able to cope with severe stress without therapy. But what defines the impact of severe stressors and who can cope with traumatic events and who cannot? And are all children at equal risk of getting exposed to these events, or can we distinguish factors that predict the likelihood of becoming a victim? 

Is epidemiological research of value?

Epidemiological research, the study of the distribution and patterns of mental and physical health and their causes or influences in a population, may help us to answer these questions. Nonetheless, epidemiological studies on stress and trauma tend to struggle with one major methodological limitation: when looking at severe stress, researchers are likely to end up with only a very small percentage of traumatised children. The statistical power to detect associations between precursors of trauma and the occurrence of the events, or between the events and subsequent mental health problems, is small. The question that consequently rises is whether this implies that epidemiology is the wrong way to study stress and trauma or at least inferior to on-spot studies focusing on clinical samples? I would say no. 

Insight in resilience

First, even though significant associations can be difficult to detect (because they are only valid for subgroups of a sample), findings can be meaningful. Whereas most children and adolescents exposed to severe stress will experience consequences in one way or another, we can detect those fortunate kids who are all right. More importantly, an epidemiological approach can help us to gain insight in factors that make these children resilient, whether these are relatively flexible (and therefore a potential subject for intervention research) or more irreversible (i.e., genetic factors). For example, in a study using data from the longitudinal cohort study TRAILS, we studied how children differed in their sensitivity to childhood stress, dependent on their genotypes1. Results showed that certain genotypes could be distinguished that made children more sensitive to stress, whereas other genotypes made children being less affected by exposure. 

Learning from milder stressful events

Secondly, in epidemiological studies, and in the absence of focus groups, we often have the opportunity to define our own construct of stressful events or trauma. We can make inclusion criteria more strict or loosen them somewhat, depending on the research questions. Using a broader interpretation of trauma and including somewhat milder stressful events, more children will be ‘affected’. Consequently, we cannot only study inter-individual differences in the consequences of stress, but also study topics as stress sensitisation and cumulative effects. 

Or should we be more sceptical?

Sceptics might say that only really traumatic events (i.e., abuse), and not the milder stressful events, have serious and enduring consequences for children’s and adolescents’ development and well-being. Perhaps they are right. However, it seems that even relatively mild stressful events can result in surprising deviations from normative development. For example, we studied the association between both mild (end of a friendship, being thrown out of the parental home etc.) and more severe (i.e., loss of a parent) stressful events and personality development – a precursor of many aspects of mental health2. Whereas adolescents’ normative personality development seems to be mainly in the direction of maturation (e.g., lower fear, shyness, more effortful control), adolescents exposed to stressful events showed less maturation or even the reverse of maturation of their personality. Moreover, for all personality traits under study, a cumulative effect (linear trend) was found consistently; the more stressful events adolescents experienced, the stronger their personality change deviated from normative development.

Reciprocity of exposure and psychological problems

These are not the only findings highlighting the importance of relatively mild stress in children’s psychological development. Using data from a British epidemiological study, we studied associations between stress exposure and psychological problems3. As expected, exposure to stress predicted the development of psychological problems. But in addition to that, we found that the association between stress and problems was reciprocal. That is, being exposed to stress did not only predict later problems, but was also predicted by psychological problems prior to the event. This suggests that children may not be at equal risk of getting exposed to stressful events.

Questions that remain

What we do not know yet, is whether the established associations are short term, long lasting or irreversible. And what about the implications? Even if we can find factors that account for high resilience in traumatized -but healthy- kids, can we translate this relatively fundamental research to intervention? Of course, these are just some of the questions that remain. Nonetheless, I would argue that epidemiological studies are a valuable way to study the gray area between a stress-free, uncomplicated, youth and severe trauma. It can help us reaching and studying those that might need help but do not ask for it, as well as the resilient kids who just do not need help.


  1. Nederhof, E., Bouma, E., Riese, H., Laceulle, O., Ormel, J., & Oldehinkel, A. (2010). Evidence for plasticity genotypes in a gene-gene-environment interaction: the TRAILS study Genes, Brain and Behavior, 9 (8), 968-973 DOI: 10.1111/j.1601-183X.2010.00637.x
  2. Laceulle, O., Nederhof, E., Karreman, A., Ormel, J., & Aken, M. (2011). Stressful Events and Temperament Change during Early and Middle Adolescence: The TRAILS Study European Journal of Personality DOI: 10.1002/per.832
  3. Laceulle, O.M., O’Donnell, K., Glover, V., O’Connor, G.O., Ormel, J., van Aken, M.A.G., & Nederhof, E., (submitted). Stressful events and psychological difficulties: testing alternative candidates for sensitivity.


5 thoughts on “Epidemiology: A valuable way to study individual differences in risk and resiliency?

  1. Mjög áhugavert að sjá að börn eru mis viðkvæm fyrir streitu. Sum þola mjög lítið til að afleiðingar verði slæmar, önnur þola mikið og fá litlar afleiðingar. Hvernig get ég vitað hvað á við um mitt barn?

    • If I understand your question well, I agree that it can be difficult to know what is true for an individual child. The results from the papers I referred to are based on groups of children and reflect trends. Although interventions are often based on research with groups, individual circumstances should always be taken into account when working with traumatized children.

  2. Dr. Laceulle,

    I’m so impressed! You will be schooling PHD students and Professors yourself very soon as the world authority on epidemiological psychology! You know there is an organization here in Richmond (maybe in the country and world) called “Child Saver’s”. Child Saver’s does exactly what you are studiing and treating – Child witnessing tarumatic events and the intervention recovery to such events! When you come to Richmond next time (soon? .. Harvard?) I will introduce you to all of the key people there!

    Keep up the great work …. I cease to be impressed!

    Dave 🙂

  3. I find with my clients that they often have no conscious recollection of the traumatic events that encouraged their perceptions/cognitive processes/ behaviour patterns to become rigid, and I can certainly track my own pathology back to before the time I developed explicit memories.

    I believe the incidence of what Judith Herman characterises as Complex PTSD is a lot more common than is generally accepted (even by those affected), and I perceive a causal link between categories of trauma and clusters of maladaptive personality processes…

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