Intracluster correlation coefficients from school-based cluster randomized trials of interventions for improving health outcomes in pupils.

BACKGROUND AND OBJECTIVES: To summarize intracluster correlation coefficient (ICC) estimates for pupil health outcomes from school-based cluster randomized trials (CRTs) across world regions and describe their relationship with study design characteristics and context. METHODS: School-based CRTs reporting ICCs for pupil health outcomes were identified through a literature search of MEDLINE (via Ovid). ICC estimates were summarized both overall and for different categories of study characteristics. RESULTS: Two hundred and forty-six articles reporting ICC estimates were identified. The median (interquartile range) ICC was 0.031 (0.011 to 0.08) at the school level (N = 210) and 0.063 (0.024 to 0.1) at the class level (N = 46). The distribution of ICCs at the school level was well described by the beta and exponential distributions. Besides larger ICCs in definitive trials than feasibility studies, there were no clear associations between study characteristics and ICC estimates. CONCLUSION: The distribution of school-level ICCs worldwide was similar to previous summaries from studies in the United States. The description of the distribution of ICCs will help to inform sample size calculations and assess their sensitivity when designing future school-based CRTs of health interventions.

Systematic review of the characteristics of school-based feasibility cluster randomised trials of interventions for improving the health of pupils in the UK.

BACKGROUND: The last 20 years have seen a marked increase in the use of cluster randomised trials (CRTs) in schools to evaluate interventions for improving pupil health outcomes. Schools have limited resources and participating in full-scale trials can be challenging and costly, given their main purpose is education. Feasibility studies can be used to identify challenges with implementing interventions and delivering trials. This systematic review summarises methodological characteristics and objectives of school-based cluster randomised feasibility studies in the United Kingdom (UK). METHODS: We systematically searched MEDLINE from inception to 31 December 2020. Eligible papers were school-based feasibility CRTs that included health outcomes measured on pupils. RESULTS: Of 3285 articles identified, 24 were included. School-based feasibility CRTs have been increasingly used in the UK since the first publication in 2008. Five (21%) studies provided justification for the use of the CRT design. Three (13%) studies provided details of a formal sample size calculation, with only one of these allowing for clustering. The median (IQR; range) recruited sample size was 7.5 (4.5 to 9; 2 to 37) schools and 274 (179 to 557; 29 to 1567) pupils. The most common feasibility objectives were to estimate the potential effectiveness of the intervention (n = 17; 71%), assess acceptability of the intervention (n = 16; 67%), and estimate the recruitment/retention rates (n = 15; 63%). Only one study was used to assess whether cluster randomisation was appropriate, and none of the studies that randomised clusters before recruiting pupils assessed the possibility of recruitment bias. Besides potential effectiveness, cost-effectiveness, and the intra-cluster correlation coefficient, no studies quantified the precision of the feasibility parameter estimates. CONCLUSIONS: Feasibility CRTs are increasingly used in schools prior to definitive trials of interventions for improving health in pupils. The average sample size of studies included in this review would be large enough to estimate pupil-level feasibility parameters (e.g., percentage followed up) with reasonable precision. The review highlights the need for clearer sample size justification and better reporting of the precision with which feasibility parameters are estimated. Better use could be made of feasibility CRTs to assess challenges that are specific to the cluster design. TRIAL REGISTRATION: PROSPERO: CRD42020218993.

Characteristics and practices of school-based cluster randomised controlled trials for improving health outcomes in pupils in the United Kingdom: a methodological systematic review.

BACKGROUND: Cluster randomised trials (CRTs) are increasingly used to evaluate non-pharmacological interventions for improving child health. Although methodological challenges of CRTs are well documented, the characteristics of school-based CRTs with pupil health outcomes have not been systematically described. Our objective was to describe methodological characteristics of these studies in the United Kingdom (UK). METHODS: MEDLINE was systematically searched from inception to 30th June 2020. Included studies used the CRT design in schools and measured primary outcomes on pupils. Study characteristics were described using descriptive statistics. RESULTS: Of 3138 articles identified, 64 were included. CRTs with pupil health outcomes have been increasingly used in the UK school setting since the earliest included paper was published in 1993; 37 (58%) studies were published after 2010. Of the 44 studies that reported information, 93% included state-funded schools. Thirty six (56%) were exclusively in primary schools and 24 (38%) exclusively in secondary schools. Schools were randomised in 56 studies, classrooms in 6 studies, and year groups in 2 studies. Eighty percent of studies used restricted randomisation to balance cluster-level characteristics between trial arms, but few provided justification for their choice of balancing factors. Interventions covered 11 different health areas; 53 (83%) included components that were necessarily administered to entire clusters. The median (interquartile range) number of clusters and pupils recruited was 31.5 (21 to 50) and 1308 (604 to 3201), respectively. In half the studies, at least one cluster dropped out. Only 26 (41%) studies reported the intra-cluster correlation coefficient (ICC) of the primary outcome from the analysis; this was often markedly different to the assumed ICC in the sample size calculation. The median (range) ICC for school clusters was 0.028 (0.0005 to 0.21). CONCLUSIONS: The increasing pool of school-based CRTs examining pupil health outcomes provides methodological knowledge and highlights design challenges. Data from these studies should be used to identify the best school-level characteristics for balancing the randomisation. Better information on the ICC of pupil health outcomes is required to aid the planning of future CRTs. Improved reporting of the recruitment process will help to identify barriers to obtaining representative samples of schools.

Characteristics and practices of school-based cluster randomised controlled trials for improving health outcomes in pupils in the UK: a systematic review protocol.

INTRODUCTION: Cluster randomised trials (CRTs) are studies in which groups (clusters) of participants rather than the individuals themselves are randomised to trial arms. CRTs are becoming increasingly relevant for evaluating interventions delivered in school settings for improving the health of children. Schools are a convenient setting for health interventions targeted at children and the CRT design respects the clustered structure in schools (ie, pupils within classrooms/teachers within schools). Some of the methodological challenges of CRTs, such as ethical considerations for enrolment of children into trials and how best to handle the analysis of data from participants (pupils) that change clusters (schools), may be more salient for the school setting. A better understanding of the characteristics and methodological considerations of school-based CRTs of health interventions would inform the design of future similar studies. To our knowledge, this is the only systematic review to focus specifically on the characteristics and methodological practices of CRTs delivered in schools to evaluate interventions for improving health outcomes in pupils in the UK. METHODS AND ANALYSIS: We will search for CRTs published from inception to 30 June 2020 inclusively indexed in MEDLINE (Ovid). We will identify relevant articles through title and abstract screening, and subsequent full-text screening for eligibility against predefined inclusion criteria. Disagreements will be resolved through discussion. Two independent reviewers will extract data for each study using a prepiloted data extraction form. Findings will be summarised using descriptive statistics and graphs. ETHICS AND DISSEMINATION: This methodological systematic review does not require ethical approval as only secondary data extracted from papers will be analysed and the data are not linked to individual participants. After completion of the systematic review, the data will be analysed, and the findings disseminated through peer-reviewed publications and scientific meetings. PROSPERO REGISTRATION NUMBER: CRD42020201792.