This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Bernsen, R. M. D. Articles by van der Wouden, J. C. Search for Related Content PubMed PubMed Citation Articles by Bernsen, R. M. D. Articles by van der Wouden, J. C.

Complications at Birth and Subsequent Wheeze: Risk of Attrition Bias

Rusconi and colleagues in their recent article present interesting data on associations between events during pregnancy and birth with childhood wheezing (1). However, in our opinion, the authors have not adequately addressed the issue of attrition, with possible consequent selection bias. Summarizing the study phases where attrition took place, there was an initial response rate of almost 90%, implying that there were about 2,000 nonresponders. It is not unlikely that among these nonresponders there were relatively few children with wheezing. Second, almost 1,700 questionnaires were left out of the analysis because they were not completed by the biological mother, leaving us with about 83% of the original sample. This second group is possibly also not a random selection: one could, for example, think of deceased or divorced mothers. Third, we lose another 2,700 children whose parents, have relatively little education and have reported incomplete data on wheezing and respiratory disease. Again, these are possibly children with relatively few symptoms. At this stage, about 71% of the original sample is left. Finally, more than 3,400 children were excluded because of missing answers on maternal variables or confounders. Again, we have no clue how this group differed from the remaining (roughly) 12,000 children (only 55% of the original sample!).

The prevalence of wheezing in the past 12 months found in this study is about 11%. Comparing this result with the prevalence found in Italy in the third phase of the worldwide ISAAC study (2), which was almost 8%, it appears that Rusconi and coworkers studied a sample where subjects with wheezing were overrepresented. Whether subjects with complications during pregnancy and birth were overrepresented and whether this resulted in spurious positive associations is unclear.

Roos M. D. Bernsen

United Arab Emirates University, Al Ain, United Arab Emirates

Johannes C. van der Wouden

Erasmus MC Rotterdam, Rotterdam, The Netherlands

FOOTNOTES

Conflict of Interest Statement: Neither author has a financial relationship with a commercial entity that has an interest in the subject of this manuscript.

REFERENCES

1. Rusconi F, Galassi C, Forastiere F, Bellasio M, De Sario M, Ciccone G, Brunetti L, Chellini E, Corbo G, La Grutta S, et al. Maternal complications and procedures in pregnancy and at birth and wheezing phenotypes in children. Am J Respir Crit Care Med 2007;175:16–21.[Abstract/Free Full Text]
2. Asher MI, Montefort S, Bjorksten B, Lai CK, Strachan DP, Weiland SK, Williams H; ISAAC Phase Three Study Group. Worldwide time trends in the prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and eczema in childhood: ISAAC phases one and three repeat multicountry cross-sectional surveys. Lancet 2006;368:733–743.[CrossRef][Medline]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Bernsen, R. M. D. Articles by van der Wouden, J. C. Search for Related Content PubMed PubMed Citation Articles by Bernsen, R. M. D. Articles by van der Wouden, J. C.