American Journal of Epidemiology Advance Access originally published online on September 12, 2006
American Journal of Epidemiology 2006 164(9):917; doi:10.1093/aje/kwj304
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Letter to the Editor |
THE AUTHORS REPLY
1 Academic Unit of Psychiatry, Department of Community Based Medicine, University of Bristol, Bristol BS8 1AU, United Kingdom
2 Academic Unit of Primary Health Care, Department of Community Based Medicine, University of Bristol, Bristol BS6 6JL, United Kingdom
3 Avon Longitudinal Study of Parents and Children, Department of Community Based Medicine, University of Bristol, Bristol BS8 1TQ, United Kingdom
4 Department of Social Medicine, University of Bristol, Bristol BS8 2PR, United Kingdom
5 Academic Centre for Child and Adolescent Health, Department of Community Based Medicine, University of Bristol, Bristol BS6 6JS, United Kingdom
(e-mail: nicola.wiles{at}bristol.ac.uk)
We thank Obel et al. (1
) for their interest in our paper (2) and take this opportunity to discuss the points they raise.
Firstly, Obel et al. (1) suggest that a cutoff of the top 10 percent of Strengths and Difficulties Questionnaire (SDQ) scores would have been the most obvious choice for our analyses based on the availability of existing data relating SDQ scores to Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) diagnoses and, furthermore, that our choice of the top tertile will include children with "normal behavior." We specifically set out to examine the relation between fetal growth and behavioral problems in a general population sample and, as such, were interested in not only the minority of children (top 
10 percent) likely to meet diagnostic criteria. Inevitably, defining our outcome as the top tertile of SDQ scores means that we will include children with milder behavioral difficulties in our outcome group, which reflects the continuum of behavioral problems seen in the general population. Many children who have behavioral difficulties would not meet DSM-IV criteria for a recognized disorder. From an epidemiologic viewpoint, it is important to examine the relation between fetal growth and behavioral problems in terms of the full spectrum of problems seen in the general population rather than defining those with problems as the top 10 percent who are more likely to be seen in specialist clinics.
Secondly, Obel et al. (1) raise the possible influence of genetic factors on the association we observed. In our article (2), we discuss the possibility of residual confounding and highlight the fact that we adjusted for maternal size (height/weight) in an attempt to account for some of the influence of genetic factors on infant size.
ACKNOWLEDGMENTS
Conflict of interest: none declared.
References
- Obel C, Henriksen TB, Olsen J. Re: "Fetal growth and childhood behavioral problems: results from the ALSPAC cohort." (Letter). Am J Epidemiol 2006;164:916–17.
[Free Full Text] - Wiles NJ, Peters TJ, Heron J, et al. Fetal growth and childhood behavioral problems: results from the ALSPAC cohort. Am J Epidemiol 2006;163:829–37.
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  O. Klungsoyr and J. F. Nygard TWO OF THE AUTHORS REPLY Am. J. Epidemiol., November 1, 2006; 164(9): 919 - 920. [Full Text] [PDF]
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