OBJECTIVE. The study tested whether a combined environmental and educational intervention solely promoting water consumption was effective in preventing overweight among children in elementary school.
METHODS. The participants in this randomized, controlled cluster trial were second- and third-graders from 32 elementary schools in socially deprived areas of 2 German cities. Water fountains were installed and teachers presented 4 prepared classroom lessons in the intervention group schools (N = 17) to promote water consumption. Control group schools (N = 15) did not receive any intervention. The prevalence of overweight (defined according to the International Obesity Task Force criteria), BMI SD scores, and beverage consumption (in glasses per day; 1 glass was defined as 200 mL) self-reported in 24-hour recall questionnaires, were determined before (baseline) and after the intervention. In addition, the water flow of the fountains was measured during the intervention period of 1 school year (August 2006 to June 2007).
RESULTS. Data on 2950 children (intervention group: N = 1641; control group: N = 1309; age, mean ± SD: 8.3 ± 0.7 years) were analyzed. After the intervention, the risk of overweight was reduced by 31% in the intervention group, compared with the control group, with adjustment for baseline prevalence of overweight and clustering according to school. Changes in BMI SD scores did not differ between the intervention group and the control group. Water consumption after the intervention was 1.1 glasses per day greater in the intervention group. No intervention effect on juice and soft drink consumption was found. Daily water flow of the fountains indicated lasting use during the entire intervention period, but to varying extent.
CONCLUSION. Our environmental and educational, school-based intervention proved to be effective in the prevention of overweight among children in elementary school, even in a population from socially deprived areas.
Comments
Random sampling alone does not make a randomized trial
We read with great interest the article by Muckelbauer et al (1), in which the authors assessed whether a combined environmental and educational intervention (aimed at promoting water consumption) reduced the prevalence of overweight among children in elementary schools. The authors claimed that their study was a “randomized, controlled cluster trial” including 32 elementary schools (defined as the cluster units), for a total of 2950 children. However, a scrutiny of this paper led us to wonder why the authors claimed that this trial was randomized, and we think the title is misleading for Pediatrics readers.
The authors indeed specified that “randomization was performed at the city level,” but actually, only two cities were considered. Even for a cluster randomized trial, the number of randomized units has to be higher. Readers may also be confused by the school selection process the authors used. Indeed a random sample of schools from each city was selected to be included in the study. However in a randomized trial, randomization is defined as “the process of randomly allocating participants into one of the arms of a controlled trial,” (2) not as the process of selection of participants. At the end, the authors’ “randomized trial” is really a non- randomized controlled study: “[a] quantitative study estimating the effectiveness of an intervention (harm or benefit) that does not use randomisation to allocate units to comparison groups” (2). In that sense, Figure 1, which does not depict randomization, is accurate. The level of evidence of such a design is somewhat different from the level of evidence of a randomized trial, and at least, authors should have discussed this point as a limitation of their study.
To design the study as a cluster randomized trial, schools should have been randomly allocated to the intervention or the control group, after considering the city as a stratification factor. Such an approach was already used by James et al (3) in conducting a similar study. Doing so may also have prevented schools from declining participation, because consent of the school’s guardians would have been sought before the schools they were in charge of were randomized. As pointed out recently (4), such an approach is essential to prevent post-randomization withdrawal of clusters, which inevitably leads to discarding these clusters for the statistical analysis and thus induces selection bias.
1. Muckelbauer R, Libuda L, Clausen K, Toschke AM, Reinehr T, Kersting M. Promotion and provision of drinking water in schools for overweight prevention: randomized, controlled cluster trial. Pediatrics 2009;123(4):e661-7. 2. Green S, Higgins J, editors (2005) Glossary. Cochrane handbook for systematic reviews of interventions 4.2.5. Available: http://www.cochrane.org/resources/glossary.htm. Accessed 22 April 2009. 3. James J, Thomas P, Cavan D, Kerr D. Preventing childhood obesity by reducing consumption of carbonated drinks: cluster randomised controlled trial. BMJ 2004;328(7450):1237. 4. Giraudeau B, Ravaud P. Preventing bias in cluster randomised trials. PLoS Med 2009;6(5):e1000065.
Bruno Giraudeau INSERM, CIC 202, Tours, France Université François Rabelais, Tours, France CHRU de Tours, Tours, France INSERM, U738, Paris, France
and
Philippe Ravaud Assistance Publique–Hôpitaux de Paris, Hôpital Bichat, Département d’Epidémiologie, Biostatistique et Recherche Clinique, Paris, France, Université Paris 7–Denis Diderot, Paris, France INSERM, U738, Paris, France
Conflict of Interest:
None declared