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

Practical considerations for sample size calculation for cluster randomized trials

Cluster randomized trials are an essential design in public health and medical research, when individual randomization is infeasible or undesirable for scientific or logistical reasons. However, the correlation among observations within clusters leads to a decrease in statistical power compared to an individually randomised trial with the same total sample size. This correlation - often quantified using the intra-cluster correlation coefficient - must be accounted for in the sample size calculation to ensure that the trial is adequately powered. In this paper, we first describe the principles of sample size calculation for parallel-arm CRTs, and explain how these calculations can be extended to CRTs with cross-over designs, with a baseline measurement and stepped-wedge designs. We introduce tools to guide researchers with their sample size calculation and discuss methods to inform the choice of the a priori estimate of the intra-cluster correlation coefficient for the calculation. We also include additional considerations with respect to anticipated attrition, a small number of clusters, and use of covariates in the randomisation process and in the analysis.

Statistical analysis plan for a cluster randomised controlled trial to compare screening, feedback and intervention for child anxiety problems to usual school practice: identifying Child Anxiety Through Schools-identification to intervention (iCATS-i2i)

BACKGROUND

The Identifying Child Anxiety Through Schools-identification to intervention (iCATS-i2i) trial is being conducted to establish whether 'screening and intervention', consisting of usual school practice plus a pathway comprising screening, feedback and a brief parent-led online intervention (OSI: Online Support and Intervention for child anxiety), bring clinical and health economic benefits compared to usual school practice and assessment only - 'usual school practice', for children aged 8-9 years in the following: (1) the 'target population', who initially screen positive for anxiety problems according to a two-item parent-report child anxiety questionnaire - iCATS-2, and (2) the 'total population', comprising all children in participating classes. This article describes the detailed statistical analysis plan for the trial.

METHODS AND DESIGN

iCATS-i2i is a definitive, superiority, pragmatic, school-based cluster randomised controlled trial (with internal pilot), with two parallel groups. Schools are randomised 1:1 to receive either screening and intervention or usual school practice. This article describes the following: trial objectives and outcomes; statistical analysis principles, including detailed estimand information necessary for aligning trial objectives, conduct, analyses and interpretation when there are different analysis populations and outcome measures to be considered; and planned main analyses, sensitivity and additional analyses.

TRIAL REGISTRATION

ClinicalTrials.gov ISRCTN76119074. Registered on 4 January 2022.

Does Implementation Matter? Associations Between Implementation of Maine's Anti- Bullying Law and Bullying Victimization Among High School Youth

PURPOSE

To characterize the relationship between implementation of an antibullying law and bullying rates among high school youth.

METHODS

School staff (administrators, counselors, and teachers) from public high schools in Maine completed a survey assessing: (1) the frequency with which they implemented 17 components of their district's antibullying policy as mandated by state law; and (2) confidence in implementing the law. Their responses were linked to data on bullying victimization among high school respondents to the Maine Integrated Youth Health Survey, which created a population-based dataset of 84 high schools with 29,818 student responses.

RESULTS

Students in schools where administrators (adjusted odds ratio = 0.93; 95% CI: 0.89, 0.97) and counselors (adjusted odds ratio = 0.86; 95% CI: 0.81, 0.92) reported implementing more mandated components of the law experienced notable reductions in the odds of bullying, controlling for student-level characteristics (sex, race, grade) and for school-level bullying rates assessed prior to the passage of the law. With respect to specific implementation components, bullying was most consistently reduced in schools where staff reported increased referrals for counseling and other supports for targets of bullying and in schools where counselors and teachers were interviewed as part of bullying investigations. Students in schools where teachers reported increased confidence in implementing the antibullying law also had reduced odds of bullying.

DISCUSSION

These data provide some of the first evidence that the efficacy of a state's antibullying law depends in part on the extent to which school personnel implement the law.