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Sample size calculation

SA Saskia Antwerpes
MC Marie Costa
MC Marion Coste
MB Morgane Bureau
GM Gwenaelle Maradan
CC Christophe Cutarella
JL Jacques Leloutre
OR Olivier Riccobono-Soulier
SH Sophie Hedoire
EF Elodie Frot
FV Fabienne Vernier
SV Stéphanie Vassas-Goyard
TB Tangui Barré
DC Danielle Casanova
PC Patrizia Carrieri
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The CSAPA delivering the intervention could not enrol more than 25–30 persons per year. Accordingly, in order to avoid overly prolonging the study and to ensure adequate power, we decided to include twice as many controls than intervention participants. As there are no comparative estimates in the literature to predict the natural variation in the number of alcohol-related harms over follow-up after a TPE intervention, the sample size was computed according to the following assumptions: (1) the Choizitaconso TPE programme will be considered effective if it results in a reduction of at least 30% in the number of alcohol-related harms in the intervention group vs. an expected 5% reduction in the control group over a 6-month period. With an alpha = 0.05 and a power of 80%, we estimated we would need 30 individuals in the intervention group and 60 in the control group to be able to demonstrate a significant difference between both groups.

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