Effect sizes and intra-cluster correlation coefficients measured from the Green Dot High School study for guiding sample size calculations when designing future violence prevention cluster randomized trials in school settings.

PURPOSE: Cluster randomized controlled trials (cRCTs) are popular in school-based research designs where schools are randomized to different trial arms. To help guide future study planning, we provide information on anticipated effect sizes and intra-cluster correlation coefficients (ICCs), as well as school sizes, for dating violence (DV) and interpersonal violence outcomes based on data from a cRCT which evaluated the bystander-based violence intervention 'Green Dot'. METHODS: We utilized data from 25 schools from the Green Dot High School study. Effect size and ICC values corresponding to dating and interpersonal violence outcomes are obtained from linear mixed effect models. We also calculated the required number of schools needed for future studies utilizing available methods that do and do not consider variation in school size. RESULTS: Observed effect sizes for DV outcomes range from 0.06 to 0.11. Observed ICC values for DV outcomes range from 0.0006 to 0.0032. The upper limit of 95% CIs for the true ICCs range from 0.0023 to 0.0070. CONCLUSION: School-based evaluations with violence outcomes are expected to have small effect sizes. Observed ICCs are less than 0.005 and upper limit of of 95% CIs for the true ICCs are less than 0.01. Designing school-based cRCTs should account for the ICC, even if its value is assumed to be negligible. Furthermore, variation in school sizes should also be accounted for to avoid having too few schools to achieve the desired power.

Direct notification of cervical cytology results to women improves follow-up in cervical cancer screening - A cluster-randomised trial.

Up to half of all women do not receive follow-up as recommended after cervical cytology testing and are thus at increased risk of dysplasia progression. Women from lower social positions are at increased risk of not receiving follow-up. Sample takers, often general practitioners, convey results to women, but communication problems constitute a challenge. We aimed to investigate the effect of direct notification of cervical cytology results on follow-up rates. In a 1:1 cluster-randomised controlled trial, we assessed if having the pathology department convey cervical cytology results directly to the investigated women improved timely follow-up, compared with conveying the results via the general practitioner as usual. All women with a cervical cytology performed in a general practice in the Central Denmark Region (2013-2014) and receiving follow-up recommendation were included (n = 11,833). The proportion of women without timely follow-up was lower in the group with direct notifications than in the control group of women receiving usual care, regardless of age, educational status, cohabitation status and ethnicity. Among the women with the most severe cervical cytology diagnoses who are recommended gynaecological follow-up within 3 months, the percentage without timely follow-up was 15.1% in the intervention group and 19.5% in the control group (prevalence difference: -0.04 (95%CI: -0.07; -0.02)). Improved timely follow-up was also observed for women with a recommendation to have follow-up performed at 3 and 12 months. Cervical cytology results conveyed directly by letter to women increased the proportion of women with timely follow-up without raising inequality in follow-up measured by social position. Trial registration: ClinicalTrials.gov (TRN: NCT02002468) 29 November 2013.