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. 2020 Jun 1;49(3):954-962.
doi: 10.1093/ije/dyz277.

Power calculations for cluster randomized trials (CRTs) with right-truncated Poisson-distributed outcomes: a motivating example from a malaria vector control trial

Lazaro M Mwandigha  1 , Keith J Fraser  1 , Amy Racine-Poon  2   3 , Mohamad-Samer Mouksassi  3   4   5   6 , Azra C Ghani  1
Affiliations

Power calculations for cluster randomized trials (CRTs) with right-truncated Poisson-distributed outcomes: a motivating example from a malaria vector control trial

Lazaro M Mwandigha et al. Int J Epidemiol. .

Abstract

Background: Cluster randomized trials (CRTs) are increasingly used to study the efficacy of interventions targeted at the population level. Formulae exist to calculate sample sizes for CRTs, but they assume that the domain of the outcomes being considered covers the full range of values of the considered distribution. This assumption is frequently incorrect in epidemiological trials in which counts of infection episodes are right-truncated due to practical constraints on the number of times a person can be tested.

Methods: Motivated by a malaria vector control trial with right-truncated Poisson-distributed outcomes, we investigated the effect of right-truncation on power using Monte Carlo simulations.

Results: The results demonstrate that the adverse impact of right-truncation is directly proportional to the magnitude of the event rate, λ, with calculations of power being overestimated in instances where right-truncation was not accounted for. The severity of the adverse impact of right-truncation on power was more pronounced when the number of clusters was ≤30 but decreased the further the right-truncation point was from zero.

Conclusions: Potential right-truncation should always be accounted for in the calculation of sample size requirements at the study design stage.

Keywords: Truncated outcomes; sample size; statistical power; vector control trial.

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Figures

Figure 1
Figure 1
Conceptual design for the attractive targeted sugar baits (ATSB) trial. The treatment clusters have ATSB feeding stations outside the houses (denoted by the green circle) in addition to insecticide-treated nets (ITNs) inside each house. The control clusters have only ITNs in the houses, the standard of care recommended by the World Health Organization (WHO). Therefore, the effect size is the efficacy of the ATSB detectable over and above that of ITNs.
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References

    1. Hayes RJ, Alexander NDE, Bennett S, Cousens SN.. Design and analysis issues in cluster-randomized trials of interventions against infectious diseases. Stat Methods Med Res 2000;9:95–116. - PubMed
    1. Hemming K, Eldridge S, Forbes G, Weijer C, Taljaard M.. How to design efficient cluster randomized trials. BMJ 2017;358:j3064. - PMC - PubMed
    1. Vontas J, Moore S, Kleinschmidt I. et al. Framework for rapid assessment and adoption of new vector control tools. Trends Parasitol 2014;30:191–204. - PubMed
    1. Wilson AL, Boelaert M, Kleinschmidt I. et al. Evidence-based vector control? Improving the quality of vector control trials. Trends Parasitol 2015;31:380–90. - PubMed
    1. Hayes RJ, Bennett S.. Simple sample size calculation for cluster-randomized trials. Int J Epidemiol 1999;28:319–26. - PubMed

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