American Journal of Epidemiology Advance Access originally published online on November 9, 2005
American Journal of Epidemiology 2006 163(1):100; doi:10.1093/aje/kwj013
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Letter to the Editor |
THE AUTHORS REPLY
1 Division of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, DK-2300 Copenhagen S, Denmark
2 Department of Biostatistics, University of Copenhagen, DK-2200 Copenhagen N, Denmark
(e-mail: twe{at}ssi.dk)
We thank Dr. Bernsen for her thoughtful comments (1
) on our study (2) and find her proposed explanation for our findings with respect to the effect of younger siblings on the risk of allergic rhinitis interesting.
However, we find that there are several factors that speak against the proposal. First of all, allergic rhinitis is rarely so devastating that it would prompt parents to have fewer subsequent children than they might otherwise have planned. Second, although some cases appear in early childhood, most cases do not debut until the second decade of life, at which point many families already have the desired number of children. Consequently, allergic rhinitis in a child is likely to have little influence on family size.
Under the proposed theory by Bernsen (1), the diagnosis of allergic rhinitis in one child could prompt parents not to have additional children. As a result, children who are much older than their next youngest siblings would be expected to have a reduced risk of allergic rhinitis. Thus, despite a long period of "follow-up," allergic rhinitis did not develop and so parents proceeded to have the next child as planned. However, a large intersibling age difference was not associated with a reduced risk of allergic rhinitis in our study, as analyzed previously (1). The same was true when we restricted the analysis on age interval to closest younger sibling to subjects with at least one older sibling (analysis for this letter).
In conclusion, we still find, as argued in the paper (2), that postnatal mechanisms are the most plausible explanation for the observed reduced risk of allergic rhinitis associated with having younger siblings.
ACKNOWLEDGMENTS
Conflict of interest: none declared.
References
- Bernsen RMD. Re: "Sibship characteristics and risk of allergic rhinitis and asthma." (Letter). Am J Epidemiol 2006;163:99–100.
[Free Full Text] - Westergaard T, Rostgaard K, Wohlfahrt J, et al. Sibship characteristics and risk of allergic rhinitis and asthma. Am J Epidemiol 2005;162:125–32.
[Abstract/Free Full Text]
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