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Sample size calculator for cluster randomized trials

Health Services Research Unit, University of Aberdeen, Polwarth Building Foresterhill, Aberdeen, Scotland AB25 2ZD UK.
Computers in Biology and Medicine (Impact Factor: 1.46). 04/2004; 34(2):113-25. DOI: 10.1016/S0010-4825(03)00039-8
Source: PubMed

ABSTRACT Cluster randomized trials, where individuals are randomized in groups are increasingly being used in healthcare evaluation. The adoption of a clustered design has implications for design, conduct and analysis of studies. In particular, standard sample sizes have to be inflated for cluster designs, as outcomes for individuals within clusters may be correlated; inflation can be achieved either by increasing the cluster size or by increasing the number of clusters in the study. A sample size calculator is presented for calculating appropriate sample sizes for cluster trials, whilst allowing the implications of both methods of inflation to be considered.

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    • "These interventions were selected because they are the most effective based on their effect sizes [3] [14] [17], yet the least used [9] [20] [21]. Based on a control group mean number of interventions = 0.1, SD = 0.3 [20], D = 0.5, intracluster correlation coefficient = 0.6 [2], a = 0.05, and b = 0.8, 136 participants were required, equivalent to 14 classes, with up to 10 participants/class. The sample size was doubled to 28 classes to account for fewer individuals/class and losses to follow-up. "
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    ABSTRACT: Educating parents about ways to minimize pain during routine infant vaccine injections at the point of care may positively impact on pain management practices. The objective of this cluster randomized trial was to determine the impact of educating parents about pain in outpatient pediatric clinics on their use of pain treatments during routine infant vaccinations. Four hospital-based pediatric clinics were randomized to intervention or control groups. Parents of 2- to 4-month-old infants attending the intervention clinics reviewed a pamphlet and a video about vaccination pain management on the day of vaccination, whereas those in the control clinics did not. Parent use of specific pain treatments (breastfeeding, sugar water, topical anesthetics, and/or holding of infants) on the education day and at subsequent routine vaccinations 2 months later was the primary outcome. Altogether, 160 parent-infant dyads (80 per group) participated between November 2012 and February 2014; follow-up data were available for 126 (79%). Demographics did not differ between groups (P > 0.05). On the education day and at follow-up vaccinations, use of pain interventions during vaccinations was higher in the intervention group (80% vs 26% and 68% vs 32%, respectively; P < 0.001 for both analyses). Educating parents about pain management in a hospital outpatient setting leads to higher use of pain interventions during routine infant vaccinations.
    Pain 01/2015; 156(1):185-91. DOI:10.1016/j.pain.0000000000000021 · 5.84 Impact Factor
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    • "These interventions were selected because they are the most effective based on their effect sizes [3] [14] [17], yet the least used [9] [20] [21]. Based on a control group mean number of interventions = 0.1, SD = 0.3 [20], D = 0.5, intracluster correlation coefficient = 0.6 [2], a = 0.05, and b = 0.8, 136 participants were required, equivalent to 14 classes, with up to 10 participants/class. The sample size was doubled to 28 classes to account for fewer individuals/class and losses to follow-up. "
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    • "Randomization was stratified by practice size in single working GPs, duo practices and group practices with three or more GPs. Despite the imposed sample size, we performed a power calculation [21]. With a significance level of 0.05 and assumed intra-cluster coefficient of 0.1, we calculated that 114 clusters with a cluster size of 20 gave 80% power to detect between AQIP and UQIP a 10% absolute difference in the proportion of patients achieving a 10% improvement in the primary biochemical endpoints. "
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