American Journal of Epidemiology Advance Access originally published online on September 17, 2007
American Journal of Epidemiology 2007 166(10):1138-1139; doi:10.1093/aje/kwm253
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Pesonen et al. Respond to "The Life Course Epidemiology of Depression"
1 Department of Psychology, University of Helsinki, Helsinki, Finland
2 National Public Health Institute, Helsinki, Finland
3 Department of Public Health, University of Helsinki, Helsinki, Finland
Correspondence to Dr. Katri Räikkönen, Department of Psychology, University of Helsinki, P.O. Box 9, Siltavuorenpenger 20 R, Helsinki FI-00014, Finland (e-mail: katri.raikkonen{at}helsinki.fi).
Received for publication July 10, 2007. Accepted for publication August 13, 2007.
In his insightful commentary on our recent publication (1), Gilman (2) mentions three potential challenges with implications for life-course research.
First, confounders related to unobserved factors are of major importance in all scientific research. Exceptional conditions, such as in Finland during World War II, are comparable to major environmental disasters. They are particularly significant to natural experimental designs because potential confounders are assumed to be randomly distributed across the groups under investigation. The likelihood of a Finnish child being evacuated was influenced by an unpredictable interplay between political and intrafamilial factors, such as the parents generally choosing to send only one or some children away (3). Despite Gilman's view (2), the evacuations were voluntary, not under "mandatory evacuation orders." In 1942, when the first massive wave of evacuations took place, the war was also expected to end quickly. In response to Gilman's concern, we did not find that parental socioeconomic status influenced the route of evacuation, either through the governmental system or other contacts (p > 0.27).
Even child mental health professionals advocated the evacuations (4, 5), creating the sense that this was an opportunity for children, as Finnish child psychiatrist T. Brander pertinently remarked in 1943:
Not a single case has come to my attention in which a child suffered psychological injury from this voluntary evacuation. Quite the contrary: such a stay proved to be an instructive and refreshing experience, from which the children returned with heightened vitality. This was due to the excellent care and attention bestowed on our children by our western neighbours (4, p. 314).
As to the second challenge of sampling bias, approximately 11 percent of the children were adopted in Sweden (3). A previous study (6) found no significant differences in mental health status between the adopted and returned former child evacuees. In addition to adoptions, the migration processes between Sweden and Finland have been relatively complex, some adopted children moving back to Finland as they grew up, and some former evacuees moving back to Sweden as young adults. The mortality of evacuated children was 0.6 percent over the whole evacuation period (mean: 2.1 years), slightly lower than the annual mortality among Finnish children aged 1–9 years, which ranged from 0.4 percent to 0.5 percent during 1941–1945 (7). We acknowledge that the parents may have generally chosen the weakest child(ren), causing potential bias (8). However, the original governmental policy aimed at excluding unhealthy children. Later in the war, sick children (11 percent of registered evacuations, 3.5 percent mortality) were also considered eligible for evacuation (3). (Note: The statistics on adoption and mortality during evacuation are based on the register in the Finnish National Archives (48,628 evacuated children).)
Third, Gilman (2) claims that model specification is a challenge to causal inference. As many studies report, our study found higher educational attainment to be associated with fewer depressive symptoms (age-adjusted r = –0.11, p = 0.001). The effect of education on depressive symptoms remained even when it was entered into a regression equation simultaneously with the evacuation variable but, unlike Räsänen (9) in a previous study, we found no statistical evidence of an association between evacuation and adult educational attainment (p = 0.81) nor did educational attainment mediate between evacuation and depressive symptoms.
Finally, we agree with Gilman that the evacuated children may have experienced other adversities during their foreign stay, making it difficult to isolate the effect of separation from other influences. However, the children lost their secure base with the unpredictable evacuation (10) and, thus, the parental assistance needed in regulating emotions, especially under serious stress. As a subjective case report brought up by Gilman describes (11), the separation trauma evoked both dissociative memory function and uncontrollable anxiety, which characterized individual emotion regulation even 50 years after evacuation. Importantly, the former child evacuees in the Kuopio study (n = 379) (6) reported more distress symptoms, fears, and obsessive thoughts than did their controls (n = 144), although there were no differences in clinical mental health status among subgroups of 30 individuals.
To conclude, we must carefully reflect upon the quality of the nature in natural experiments. Until now, we have found no systematic trends in the selection of the children, but we acknowledge that exploration of these trends, also beyond the existing data, is crucial.
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ACKNOWLEDGMENTS |
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Conflict of interest: none declared.
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References |
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 TOP References |
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- Pesonen AK, Räikkönen K, Heinonen K, et al. Depressive symptoms in adults separated from their parents as children: a natural experiment during World War II. Am J Epidemiol (2007) 166:1126–33.
[Abstract/Free Full Text] - Gilman SE. Invited commentary: The life course epidemiology of depression. Am J Epidemiol (2007) 166:1941–7.
- Lomu J. Lastensiirtokomitea ja sen arkisto 1941 –1949. (The committee of child evacuations 1941–1949). (In Finnish) (1974) Helsinki, Finland: Finnish National Archives. (Archival code 441:5).
- Brander T. Psychiatric observations among Finnish children during Russo-Finnish war of 1939 –1940. Nerv Child (1943) 2:313–19.
- Ylppö A. Report to the Ministry of Social Affairs, January 12, 1952. (In Swedish) (1952) Helsinki, Finland: Finnish National Archives. (Archival code 441:11).
- Räsänen E. Excessive life changes during childhood and their effects on mental and physical health in adulthood. Acta Paedopsychiatr (1992) 55:19–24.[Medline]
- Annuaire statistique de Finlande. Nouvelle série, années 1946 –47. (In French) (1948) Helsinki, Finland: Bureau Central Statistique.
- Räikkönen K, Schubert C, Pesonen AK, et al. Parental reports of global physical health at ages 3 and 6 predict self-reported depressive symptoms 17-years later. Br J Dev Psychol (2004) 22:439–59.[CrossRef]
- Räsänen E. Change in culture and language environment in childhood and its effect on adult life. Acta Psychiatr Scand (1989) 80:280–6.[Web of Science][Medline]
- Bowlby J. Attachment and loss. Vol II. Separation, anxiety and anger. (1973) New York, NY: Basic Books.
- Serenius M. The silent cry. A Finnish child during World War II and 50 years later. Int Forum Psychoanal (1995) 4:35–47.
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Related articles in Am. J. Epidemiol.:
- Depressive Symptoms in Adults Separated from Their Parents as Children: A Natural Experiment during World War II
- Anu-Katriina Pesonen, Katri Räikkönen, Kati Heinonen, Eero Kajantie, Tom Forsén, and Johan G. Eriksson
Am. J. Epidemiol. 2007 166: 1126-1133.[Abstract] [FREE Full Text]
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