School-based Obesity Prevention Intervention Research Articles

Barriers and facilitators of school-based obesity prevention interventions: a qualitative study from the perspectives of primary school headteachers

BackgroundChildhood obesity is a growing global health issue. The World Health Organization identifies obesity as a significant risk factor for Non-Communicable Diseases and considers it a pandemic. This study aimed to investigate headteachers' perspectives and practices concerning childhood obesity prevention interventions in primary schools highlighting the barriers and facilitators for those interventions.MethodsThis qualitative study used a phenomenological approach and semi-structured interviews with headteachers of primary schools in the West Yorkshire area, UK. The collected data was transcribed and analysed using inductive thematic analysis.ResultsA total of 32 interviews with headteachers were conducted. The data indicated that interventions meant to prevent childhood obesity in schools are influenced by a range of barriers and facilitators that are organized under the following seven key themes: (1) staff perception of obesity prevention at school; (2) school policies on eating at schools; (3) School curriculum on healthy diets and physical activities; (4) role models at school; (5) partnership with parents; (6) extra-curricular activities on healthy diets and physical activities; (7) School capacity and resources.ConclusionsChildhood obesity prevention interventions vary across UK schools depending on staff and head teachers' beliefs, awareness, commitments, school resources, parents' involvement and parents’ awareness, income, and culture. The study suggests raising awareness of childhood obesity among parents and staff, involving external partners like school nurses for training, making all primary pupils eligible for free meals, and providing schools with guidance on securing government funding. It provides a foundation for improving school-based strategies that indirectly contribute to better health outcomes for children.

The most optimal school recruitment strategies for school-based obesity prevention and health promotion research in the United States: A systematic review with Delphi study.

This systematic review with the Delphi study aimed to identify effective and resource-efficient (optimal) strategies for recruiting schools into health promotion interventions in the United States. A literature search was conducted in PubMed, Cochrane Library, and CINAHL (EBSCO). A total of 116 interventions reported in 160 articles were included. Most school-based interventions did not report data regarding school recruitment duration (81%), target school size (63%), and school recruitment strategies (78%). Further, no details were provided regarding the reasons for declining to participate despite being eligible. For the Delphi, responses from 23 researchers in school-based clinical trials were collected. A qualitative descriptive approach was used for coding responses and collapsed into higher-order categories based on school recruitment strategies. Delphi participants reported that (1) creating new or leveraging pre-existing partnerships, (2) intervention champion, (3) minimal school disruptions, (4) working with open mind/flexibility, and (5) transparent communication are the most optimal school recruitment strategies. Staff time and travel were the most frequently reported costs for implementing those strategies. The overall trend in school-based obesity prevention intervention studies illustrates the importance of a better understanding school recruitment. Improved reporting can allow researchers to budget their time and resources better and provide greater confidence in reaching their target school size.

Improving Evidence-Synthesis for School-Based Obesity Prevention Interventions. Comment on Ginell et al. Unreliable Findings Due to Miscalculations and Errors. Comment on "Nally et al. The Effectiveness of School-Based Interventions on Obesity-Related Behaviours in Primary School Children: A Systematic Review and Meta-Analysis of Randomised Controlled Trials. Children 2021, 8, 489".

As researchers with substantial experience in the child obesity field [...].

The long-term effects of primary school-based obesity prevention interventions in children: A systematic review and meta-analysis.

This systematic review and meta-analysis investigate the long-term effects of primary school-based obesity prevention interventions on body-mass index (and z-scores), waist circumference (and z-scores) and weight status. Four databases were searched for studies from date of inception until June 8th, 2021. We included randomized controlled trials (RCT) and non-RCTs investigating effects ≥12 months post-intervention of primary school-based interventions with intervention duration ≥6 months and containing a diet and/or physical activity component on outcomes of interest. Articles were assessed on risk of bias and methodological quality by RoB2 and ROBINS-I. Meta-analysis was performed and results were narratively summarized. Evidence quality was assessed with GRADE. Nineteen studies were included, 9 were pooled in a meta-analysis. No long-term effects were found on body-mass index (+0.06 kg/m2 ; CI95%=-0.38, 0.50; I2 = 66%), body-mass index z-scores (-0.08; CI95%=-0.20, 0.04; I2 = 36%), and waist circumference (+0.57 cm; CI95%=-0.62, 1.75; I2 = 13%). Non-pooled studies reported mixed findings regarding long-term effects on body-mass index, body-mass index z-scores and weight status, and no effects on waist circumference and waist circumference z-scores. Evidence certainty was moderate to very low. No clear evidence regarding long-term effects of primary school-based interventions on obesity-related outcomes was found. Recommendations for further research and policy are discussed. Prospero registration ID: CRD42021240446.

Interventions to prevent obesity in school-aged children 6-18 years: An update of a Cochrane systematic review and meta-analysis including studies from 2015-2021.

BackgroundChildhood obesity remains a global public health priority due to the enormous burden it generates. Recent surveillance data suggests there has been a sharp increase in the prevalence of childhood obesity during the COVID-19 pandemic. The Cochrane review of childhood obesity prevention interventions (0–18 years) updated to 2015 is the most rigorous and comprehensive review of randomised controlled trials (RCTs) on this topic. A burgeoning number of high quality studies have been published since that are yet to be synthesised.MethodsAn update of the Cochrane systematic review was conducted to include RCT studies in school-aged children (6-18 years) published to 30 June 2021 that assessed effectiveness on child weight (PROSPERO registration: CRD42020218928). Available cost-effectiveness and adverse effect data were extracted. Intervention effects on body mass index (BMI) were synthesised in random effects meta-analyses by setting (school, after-school program, community, home), and meta-regression examined the association of study characteristics with intervention effect.FindingsMeta-analysis of 140 of 195 included studies (183,063 participants) found a very small positive effect on body mass index for school-based studies (SMD –0·03, 95%CI –0·06,–0·01; trials = 93; participants = 131,443; moderate certainty evidence) but not after-school programs, community or home-based studies. Subgroup analysis by age (6–12 years; 13–18 years) found no differential effects in any setting. Meta-regression found no associations between study characteristics (including setting, income level) and intervention effect. Ten of 53 studies assessing adverse effects reported presence of an adverse event. Insufficient data was available to draw conclusions on cost-effectiveness.InterpretationThis updated synthesis of obesity prevention interventions for children aged 6–18 years, found a small beneficial impact on child BMI for school-based obesity prevention interventions. A more comprehensive assessment of interventions is required to identify mechanisms of effective interventions to inform future obesity prevention public health policy, which may be particularly salient in for COVID-19 recovery planning.FundingThis research was funded by the National Health and Medical Research Council (NHMRC), Australia (Application No APP1153479).

School-based obesity prevention interventions in Latin America

ABSTRACTOBJECTIVETo evaluate the implementation and effectiveness of school-based interventions to prevent obesity conducted in Latin America and provide suggestions for future prevention efforts in countries of the region.METHODSArticles published in English, Spanish, and Portuguese between 2000 and 2017 were searched in four online databases (Google Scholar, PubMed, LILACS, and REDALYC). Inclusion criteria were: studies targeting school-aged children and adolescents (6–18 years old), focusing on preventing obesity in a Latin American country using at least one school-based component, reporting at least one obesity-related outcome, comprising controlled or before-and-after design, and including information on intervention components and/or process.RESULTSSixteen studies met the inclusion criteria. Most effective interventions (n = 3) had moderate quality and included multi-component school-based programs to promote health education and parental involvement focused on healthy eating and physical activity behaviors. These studies also presented a better study designs, few limitations for execution, and a minimum duration of six months.CONCLUSIONSEvidence-based prevention experiences are important guides for future strategies implemented in the region. Alongside gender differences, an adequate duration, and the combined use of quantitative and qualitative evaluation methods, evidence-based prevention should be considered to provide a clearer and deeper understanding of the true effects of school-based interventions.

Evaluation of a pragmatic trial of a collaborative school-based obesity prevention intervention in a low-income urban district

Broader adoption of effective school-based obesity prevention interventions is critical to the success of ongoing efforts to address the childhood obesity epidemic. School-level barriers to adopting evidence-based interventions may be overcome by empowering school-level leaders to select appropriate intervention components. We used a quasi-experimental pragmatic trial design to evaluate a tailored obesity prevention intervention in 9 schools in a mid-sized urban school district in upstate New York from fall 2013 to spring 2016. We analyzed repeated height and weight measurements from an existing district screening system on 5882 students from intervention and control schools matched using propensity score methods. We assessed diet and physical activity changes in intervention schools using surveys and direct observation. The intervention led to a change of −0.27 (p = 0.026, 95% Confidence Interval (CI): −0.51, −0.03) and −0.28 (p = 0.031, 95% CI: −0.54, −0.03) BMI units in spring 2014 and fall 2014, respectively. There were no significant differences between intervention and control from spring 2015 to spring 2016. Despite the lack of sustained effects on BMI, we demonstrated the potential of supporting school leaders in a low-income district to implement supportive policy and practice changes and of using an existing BMI screening system to reduce the burden of health promotion evaluation.

Factors affecting the dose of intervention received and the participant satisfaction in a school-based obesity prevention intervention.

This study assessed factors associated with the perceived dose of intervention received and with the participant satisfaction in a school-based obesity prevention intervention. It also explored the variance in the dose of intervention received that was at the school level. Process evaluation data from a school-based intervention study conducted in Oslo in 2007–2009 were used. A total of 542 11-year-olds from 12 intervention schools were included. A web-based questionnaire was used to collect data. Descriptive analyses and multilevel regression analyses were conducted. Females and those with medium (vs. low) parental education had higher odds of reporting a high vs. low dose of intervention received at mid-way (8 months after baseline). Perceived social capital and perceived social support for physical activity from friends at baseline were positively associated with the dose of intervention received at mid-way. Perceived social capital at mid-way was positively associated with the dose of intervention reported post-intervention (20 months after baseline). Around 20% of the variance in the perceived dose of intervention received was at the school level. Satisfaction with the intervention was high overall and higher for females for several intervention components at mid-way and at post-intervention. The factors identified in this study should be taken into consideration when planning future obesity prevention interventions among youth.

Efficacy of a school-based obesity prevention intervention at reducing added sugar and sodium in children's school lunches: the LA Health randomized controlled trial.

Background:Decreasing selection and consumption of sodium and added sugars in the school cafeteria setting is important to provide optimal nutrition to children.Objective:To determine if Louisiana (LA) Health, a school-based obesity prevention intervention, could successfully reduce children’s selection and consumption of sodium and added sugars during school lunches vs. the control group.Design:Food selection, consumption, and plate waste from student lunches (3 consecutive days) in 33 public schools in rural Louisiana were collected and analyzed using the digital photography of foods method at baseline and after a 28-month obesity prevention intervention (LA Health) beginning in 4th-6th grade (87% of children received free or reduced cost lunch). Selection and consumption of energy, added sugar, and sodium was objectively measured using digital photography of foods. Mixed models, including Race and BMI, were used to determine if change in selection and consumption differed by group.Results:Sodium decreased for selection (−233.1±89.4 mg/lunch, p=0.04) and consumption (−206.3±65.9, mg/lunch) in the intervention (vs. control) by month 18, and in consumption by month 28 (−153.5±66.9 mg/lunch, p=0.03). Change in added sugar consumption decreased in the intervention (vs. control) at month 18 (−3.7±1.6, p=0.05) and at month 28 (−3.5±1.6 tsp/lunch, p=0.05).Conclusions:LA Health decreased the amount of added sugar and sodium selected and consumed, but not plate waste, by month 28. Results highlight the importance of long-term interventions and policies targeting provision and selection to improve dietary patterns in children, with less focus on plate waste.Trial Registration:clinicaltrials.govNCT00289315https://clinicaltrials.gov/ct2/show/NCT00289315?term=LA+Health&rank=1

Using Formative Research to Develop the Healthy Me, Healthy We Campaign

Although social marketing principles have been successfully employed in school-based obesity prevention interventions, their use in early care and education (ECE) settings has been limited. This paper reports on formative research to develop Healthy Me, Healthy We ( HMHW), an innovative social marketing campaign that encourages partnership between parents and providers to foster healthy eating and physical activity in preschoolers. To guide campaign development, we consulted existing literature and identified useful theories. In addition, three focus groups with providers ( n = 17) and four with parents ( n = 20) were conducted to understand strategies used to instill healthy habits in children, perceptions of how their personal behaviors influence children, and the usefulness of parent–provider partnerships. Parents and providers recognized healthy eating and physical activity as important to the development of the “whole child.” Both groups expressed feeling great responsibility for shaping children’ habits and being a role model for healthy behaviors, particularly for healthy eating. While parents and providers felt partnership was important, areas of conflict emerged with how partnerships should be executed. There is great potential for such partnerships, but careful communication is needed to avoid triggering feelings of guilt among parents and perceptions of superiority among providers. These findings informed campaign development, which was pretested in an ECE setting. The resulting HMHW campaign is delivered by the childcare center and includes materials for classroom and home use. The campaign helps strengthen parent–provider partnerships to encourage healthy eating and physical activity habits during early childhood, a critical period in the development of lifelong health habits.

The Influence of Organizational Culture on School-Based Obesity Prevention Interventions: A Systematic Review of the Literature.

Although the influence of organizational culture has been examined on a variety of student outcomes, few studies consider the influence that culture may have on school-based obesity prevention interventions. We present a systematic review of the literature to examine how elements of organizational culture may affect the adoption, implementation, and sustainability of school-based obesity prevention interventions. Fourteen studies examining the impact of organizational-level characteristics on school-based obesity prevention interventions were identified through the online databases EBSCO (CINAHL, ERIC, Agricola), Web of Science, Medline (PubMed), and Scopus. Five themes were identified as elements of organizational culture that influence the adoption, implementation, and sustainability of school-based obesity prevention interventions: organizational response to limited resources, value placed on staff training and professional development, internal support, organizational values, and school climate. Organizational culture can greatly influence the success of school-based obesity interventions. The collection of data related to organizational-level factors may be used to identify strategies for creating and sustaining a supportive environment for obesity prevention interventions in the school setting.

Evaluation of the dissemination of SNaX, a middle school-based obesity prevention intervention, within a large US school district.

Few evidence-based school obesity-prevention programs are disseminated. We used community-based participatory research principles to disseminate an evidence-based middle-school obesity-prevention program, Students for Nutrition and eXercise (SNaX), to a large, primarily Latino, school district. In the 2014-2015 school year, we trained a district "champion" to provide training and technical assistance to schools and supplied print- and web-based materials (www.snaxinschools.org). In one district region, 18 of 26 schools agreed to participate. We evaluated the dissemination process using the Reach, Effectiveness, Adoption, Implementation, and Maintenance (RE-AIM) framework. All 18 schools implemented at least one SNaX component. Of 6,410 students who attended an informational session, 1,046 registered and 472 were selected to be Student Advocates, of whom 397 attended at least one meeting. Of 60 activities observed across schools, 77% were conducted with fidelity, but local resource constraints limited most activities to a relatively small number of Student Advocates (vs. the entire student body). Qualitative data from 46 school staff and 187 students indicated positive attitudes about the program. Teachers suggested that SNaX be implemented as part of the curriculum. In the 2015-2016 school year, 6 of the original schools continued to implement SNaX, and the champion trained 94 teachers from 57 schools districtwide. Cafeteria servings overall and fruit and vegetable servings, the primary outcomes, did not increase in SNaX schools versus matched-comparison schools. Our mixed-methods evaluation of SNaX showed acceptability and fidelity, but not effectiveness. Effectiveness may be improved by providing technical assistance to community stakeholders on how to tailor core intervention components while maintaining fidelity.

Effectiveness of the Healthy Lifestyles Programme (HeLP) to prevent obesity in UK primary-school children: a cluster randomised controlled trial

SummaryBackgroundAlthough childhood overweight and obesity prevalence has increased substantially worldwide in the past three decades, scarce evidence exists for effective preventive strategies. We aimed to establish whether a school-based intervention for children aged 9–10 years would prevent excessive weight gain after 24 months.MethodsThis pragmatic cluster randomised controlled trial of the Healthy Lifestyles Programme (HeLP), a school-based obesity prevention intervention, was done in 32 schools in southwest England. All state-run primary and junior schools in Devon and Plymouth (UK) with enough pupils for at least one year-5 class were eligible. Schools were assigned (1:1) using a computer-generated sequence to either intervention or control, stratified by the number of year-5 classes (one vs more than one) and the proportion of children eligible for free school meals (<19% [the national average] vs ≥19%). HeLP was delivered to year-5 children (ages 9–10 years) over 1 year, and included dynamic and interactive activities such as physical activity workshops, education sessions delivered by teachers with short homework tasks, drama sessions, and setting goals to modify behaviour (with parental support and one-to-one discussions with HeLP coordinators). The primary outcome was change in body-mass index (BMI) standard deviation score (SDS) between baseline and 24 months, analysed in children with BMI data available for both timepoints. This study is registered with the International Standard Randomised Controlled Trial register, number ISRCTN15811706, and the trial status is complete.FindingsBetween March 21, 2012, and Sept 30, 2013, 32 eligible schools with 1324 children were recruited, of which 16 schools (676 children) were randomly assigned to the HeLP intervention and 16 schools (648 children) to control. All schools that began the trial completed the intervention, and 1244 children (628 in intervention group and 616 in control group) had BMI data at both baseline and 24 months for the primary outcome analysis. Mean BMI SDS was 0·32 (SD 1·16) at baseline and 0·35 (1·25) at 24 months in the intervention group, and 0·18 (1·14) at baseline and 0·22 (1·22) at 24 months in the control group. With adjustment for school-level clustering, baseline BMI scores, sex, cohort, and number of year-5 classes and socioeconomic status of each school, the mean difference in BMI SDS score (intervention–control) at 24 months was −0·02 (95% CI −0·09 to 0·05), p=0·57. One parent reported an adverse event related to their child's eating and activity behaviours, but agreed for the child to continue trial participation after discussion with the chief investigator.InterpretationDespite a theoretically informed and extensively piloted intervention that achieved high levels of engagement, follow-up, and fidelity of delivery, we found no effect of the intervention on preventing overweight or obesity. Although schools are an ideal setting in which to deliver population-based interventions, school-based interventions might not be sufficiently intense to affect both the school and the family environment, and hence the weight status of children. Future research should focus on more upstream determinants of obesity and use whole-systems approaches.FundingUK National Institute for Health Research, Public Health Research Programme.

Process evaluation results of a cluster randomised controlled childhood obesity prevention trial: the WAVES study

BackgroundIncreasing prevalence of childhood obesity and its related consequences emphasises the importance of developing and evaluating interventions aimed at prevention. The importance of process evaluation in health intervention research is increasingly recognised, assessing implementation and participant response, and how these may relate to intervention success or failure. A comprehensive process evaluation was designed and undertaken for the West Midlands ActiVe lifestyle and healthy Eating in School children (WAVES) study that tested the effectiveness of an obesity prevention programme for children aged 6-7 years, delivered in 24 UK schools. The four intervention components were: additional daily school-time physical activity (PA); cooking workshops for children and parents; Villa Vitality (VV), a 6-week healthy lifestyle promotion programme run by a local football club; and signposting to local PA opportunities.MethodsData relating to six dimensions (Fidelity, Reach, Recruitment, Quality, Participant Responsiveness, Context) were collected via questionnaires, logbooks, direct observations, focus groups and interviews. Multiple data collection methods allowed for data triangulation and validation of methods, comparing research observations with teacher records. The 6-stage WAVES study model ((i) Data collection, (ii) Collation, (iii) Tabulation, (iv) Score allocation and discussion, (v) Consultation, (vi) Final score allocation) was developed to guide the collection, assimilation and analysis of process evaluation data. Two researchers independently allocated school scores on a 5-point Likert scale for each process evaluation dimension. Researchers then discussed school score allocations and reached a consensus. Schools were ranked by total score, and grouped to reflect low, medium or high intervention implementation.ResultsThe intervention was predominantly well-implemented and well-received by teachers, parents and children. The PA component was identified as the most challenging, VV the least. Median implementation score across schools was 56/75 (IQR, 51.0 - 60.8). Agreement between teacher logbooks and researcher observations was generally high, the main discrepancies occurred in session duration reporting where in some cases teachers’ estimations tended to be higher than researchers’.ConclusionsThe WAVES study model provides a rigorous and replicable approach to undertaking and analysing a multi-component process evaluation. Challenges to implementing school-based obesity prevention interventions have been identified which can be used to inform future trials.Trial registrationISRCTN97000586. 19 May 2010.

Testing an Integrated Model of Program Implementation: the Food, Health & Choices School-Based Childhood Obesity Prevention Intervention Process Evaluation.

Childhood obesity is a complex, worldwide problem. Significant resources are invested in its prevention, and high-quality evaluations of these efforts are important. Conducting trials in school settings is complicated, making process evaluations useful for explaining results. Intervention fidelity has been demonstrated to influence outcomes, but others have suggested that other aspects of implementation, including participant responsiveness, should be examined more systematically. During Food, Health & Choices (FHC), a school-based childhood obesity prevention trial designed to test a curriculum and wellness policy taught by trained FHC instructors to fifth grade students in 20 schools during 2012-2013, we assessed relationships among facilitator behaviors (i.e., fidelity and teacher interest); participant behaviors (i.e., student satisfaction and recall); and program outcomes (i.e., energy balance-related behaviors) using hierarchical linear models, controlling for student, class, and school characteristics. We found positive relationships between student satisfaction and recall and program outcomes, but not fidelity and program outcomes. We also found relationships between teacher interest and fidelity when teachers participated in implementation. Finally, we found a significant interaction between fidelity and satisfaction on behavioral outcomes. These findings suggest that individual students in the same class responded differently to the same intervention. They also suggest the importance of teacher buy-in for successful intervention implementation. Future studies should examine how facilitator and participant behaviors together are related to both outcomes and implementation. Assessing multiple aspects of implementation using models that account for contextual influences on behavioral outcomes is an important step forward for prevention intervention process evaluations.

Predictors for Persistent Overweight, Deteriorated Weight Status, and Improved Weight Status During 18 Months in a School-Based Longitudinal Cohort.

To examine predictors for persistent overweight/obesity, deteriorated weight status, and improved weight status among students who participated in a school-based obesity prevention intervention from fall 2009 to spring 2011. Longitudinal assessment of a school-based cohort was conducted to determine the characteristics of students who remained overweight/obese, improved their weight status, or showed deteriorated weight status during an 18-month period. Eleven schools in southern Indiana, northwestern Kentucky, and southeastern Illinois. N = 5309 students in 4th through 12th grade. Weight, height, and self-reported physical activity and nutrition behaviors of students were measured at baseline and 6, 12, and 18 months. SAS 9.3 was employed to examine predictors for the three different weight categories using logistic regression. Low socioeconomic status (SES) (adjusted odds ratio [AOR] = 1.56 and p < .001, AOR = 1.35 and p = .0069, respectively) and higher soda intake (AOR = 1.07 and p = .0016, AOR = 1.08 and p = .0278, respectively) increased the odds of belonging to persistent overweight/obesity (30.6%) and deteriorated weight status (6.9%), compared to the persistent nonoverweight status group. While SES is an important determinant of weight category change, students' screen time and soda consumption may be important factors. Schools and families may be able to successfully focus on these modifiable risk factors, decreasing the burden of childhood obesity.

Mediating effects of resistance training skill competency on health-related fitness and physical activity: the ATLAS cluster randomised controlled trial

The purpose of this study was to examine the mediating effect of resistance training skill competency on percentage of body fat, muscular fitness and physical activity among a sample of adolescent boys participating in a school-based obesity prevention intervention. Participants were 361 adolescent boys taking part in the Active Teen Leaders Avoiding Screen-time (ATLAS) cluster randomised controlled trial: a school-based program targeting the health behaviours of economically disadvantaged adolescent males considered “at-risk” of obesity. Body fat percentage (bioelectrical impedance), muscular fitness (hand grip dynamometry and push-ups), physical activity (accelerometry) and resistance training skill competency were assessed at baseline and post-intervention (i.e., 8 months). Three separate multi-level mediation models were analysed to investigate the potential mediating effects of resistance training skill competency on each of the study outcomes using a product-of-coefficients test. Analyses followed the intention-to-treat principle. The intervention had a significant impact on the resistance training skill competency of the boys, and improvements in skill competency significantly mediated the effect of the intervention on percentage of body fat and the combined muscular fitness score. No significant mediated effects were found for physical activity. Improving resistance training skill competency may be an effective strategy for achieving improvements in body composition and muscular fitness in adolescent boys.

Parent and child perspectives on a school-based obesity prevention intervention. The West Midlands ActiVe lifestyle and healthy Eating in School children (WAVES) study

Parent and child perspectives on a school-based obesity prevention intervention. The West Midlands ActiVe lifestyle and healthy Eating in School children (WAVES) study

A meta-analysis of school-based obesity prevention programs demonstrates limited efficacy of decreasing childhood obesity

Childhood obesity is a global concern. The objectives of this meta-analytical study were to evaluate the effectiveness of school-based childhood obesity prevention programs, and to examine program components (moderators). The methods included searching databases (PubMed, Google Scholar, and the university's EBSCOhost Web service) as well as handsearching reference lists of articles published in English. Selection criteria for studies to be included in the meta-analysis were limited to studies that reported body mass index (BMI) or skinfold thickness as outcome measures and were school-based obesity prevention interventions; cross-sectional design studies were excluded. We hypothesized the meta-analysis would yield a summary effect size of magnitude which would indicate that school-based interventions have been effective in improving children's BMI or skinfold thickness values. A total of 26 114 children from 27 school-based childhood obesity prevention programs provided 54 effect sizes. A random-effects model calculated a small summary effect size of 0.039 (95% confidence interval −0.013 to 0.092). Heterogeneity among studies was observed which disappeared after pooling studies that used a randomized controlled trial design with one program moderator (physical activity or nutrition). We failed to accept our hypothesis and concluded that overall, school-based interventions have not been effective for improving body mass index or skinfold thickness to curb childhood obesity; however, randomized controlled trials that focused on physical activity or nutrition appeared to produce promising results.

Comment on “School-Based Obesity Prevention Intervention in Chilean Children: Effective in Controlling, but not Reducing Obesity”

We read with interest the article “School-Based Obesity Prevention Intervention in Chilean Children: Effective in Controlling, but not Reducing Obesity” [1], hereafter “the article.” In the article [1], nine schools were randomized into intervention and control groups according to the socioeconomic conditions of the children (a stratified randomization design at the cluster level), resulting in five schools in the intervention condition and four schools in the control. The intervention consisted of training teachers to deliver content on healthy eating and to improve the quality of physical education classes. The primary outcome was change in BMI Z score between baseline and follow-up. This is a typical cluster randomized controlled trial (cRCT) in which the inferences are intended to apply at the individual (student) level while randomization is at the cluster (school) level [2, 3]. In cRCTs, the potential lack of independence among individuals in the same cluster, that is, intracluster correlation (ICC), creates special methodological issues in both design and analysis. Any individual level analysis without considering the clustering is invalid [3]. Unfortunately, the article [1] ignored the clustering in its sample size estimation and final data analysis, which potentially increased type I and type II error rates and put their conclusions in doubt. The article [1] claims the study as a cluster randomized trial; however, the power and sample size estimation in Section 2.1 completely ignores the facts that (1) the sample size of cRCTs consists of cluster number (K) and cluster size (m), (2) the power is more dependent on the cluster number than cluster size [2], and (3) the “design effect” is caused by the similarity of individuals in the same cluster [2, 3]. The presentation of study sample sizes described in Section 2.1 is therefore misleading and might confuse readers. More severely, ignoring the clustering in the final data analyses of cRCTs (as done in the article [1]) will cause inflated type I error rates by (1) underestimating the variance of intervention effects and (2) using the extremely magnified degrees of freedom (df) in the hypothesis testing. The fact that clusters are nested within intervention conditions makes the df available to estimate the intervention effects much smaller than the df without nested clusters. For a hypothetical cRCT with m persons nested within K clusters across c experimental conditions, there will be N = c∗K∗m total persons. Because of the impact of clustering, the df for estimating the between cluster variance is the number of conditions multiplied by the number of clusters minus one, or df = c∗(K − 1), which is far smaller than c∗(K∗m − 1), used in the article [1]. Considering only nine schools that are involved in the trial, the Kenward-Roger small sample df approximation [4] should also be recommended, which has been implemented in some commercial statistical packages including SAS and R. Furthermore, in order to improve the transparency and utility of cRCTs, the CONSORT 2010: extension to cluster randomized trials [5], states that the ICC and an indication of its uncertainty are to be reported in describing (1) how the sample size is determined and (2) how clustering is taken into account in the statistical analysis. In addition, the reported ICCs are also helpful for those who may subsequently perform similar (replication) studies. To evaluate the validity of this study, we conducted a permutation/randomization test for the difference in change of BMI Z scores, using the data in Table 2. Although the major conclusion of the study—in which the school-based treatment prevented increase in BMI Z scores compared to control schools—does have statistical merit (permutation P < 0.03), we suggest that the authors redo their analyses taking the clustering into account and report the unconditional ICC (or constituent variance components) and its confidence interval for better practice.