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Nestlé Research Center
CH-1000 Lausanne 26 Switzerland
* To whom correspondence should be addressed. E-mail: dominik.grathwohl{at}rdls.nestle.com.
Dear Editor,
The article by Arslanoglu et al. (1) on the protective effect of prebiotic oligosaccharides against infection in formula-fed infants stated that "The primary outcome measures were infectious episodes, number of infections requiring antibiotics and incidence of infections." In their introduction, the authors made reference to one of their earlier studies (2) that showed that the same prebiotic short chain galactooligosaccharide/long chain fructo-oligosaccharide mixture (8 g/L of formula) "led to a significant decrease of the cumulative incidence of atopic dermatitis at 6 mo of age in a group of term infants with a family history of atopy." It is likely that the source of data for both articles was the same, because both studies examined the same product in the same population (inclusion criteria) at the same hospital during the same enrolment period. However, it is important that the authors clarify whether or not the source of data for both articles was indeed the same.
In the earlier article (2), the authors stated that "Sample size was calculated based on analysis of the previous years' incidence of atopic dermatitis in the hospital and assuming an effect size similar to that reported for probiotics." Thus, one can conclude that the primary outcome in this study was atopic dermatitis. However, if the source of data was the same for both articles but different primary outcome variables were planned, it was not stated in either article how the authors controlled for false positive rate [see International Conference of Harmonisation, Guideline on Statistical Principles for Clinical Trials, (ICH E9)] (3).
The interpretation of a clinical trial depends, among other things, on the statistical principles. If more than one primary outcome was used to assess the primary objective of the trial, the effect on type I error (false positive rate) should be explained and the method of controlling type I error should be given in the protocol (ICH E9). In the scientific community, it is generally agreed that for primary outcomes the experiment-wise false positive rate is controlled on the 5% level. Only primary outcomes provide firm evidence in support of claims (ICH E9). I recommend to the Editor that the number of primary outcomes and the statistical method used to control the false positive rate on primary outcomes be clarified by Arslanoglu et al. (1).
Manuscript received 12 March 2008.
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LITERATURE CITED |
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 TOP LITERATURE CITED |
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1. Arslanoglu S, Moro GE, Boehm G. Early supplementation of prebiotic oligosaccharides protects formula-fed infants against infections during the first 6 months of life. J Nutr. 2007;137:2420–4.
2. Moro G, Arslanoglu S, Stahl B, Jelinek J, Wahn U, Boehm G. A mixture of prebiotic oligosaccharides reduces the incidence of atopic dermatitis during the first six months of age. Arch Dis Child. 2006;91:814–9.
3. International Conference on Harmonisation E9 Expert Working Group. Statistical principles for clinical trials. International Conference on Harmonisation E9 Expert Working Group. Stat Med. 1999;18:1905–42.[Medline]
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