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Sample size

LH Lukas Higi
RS Raffael Schmitt
KK Karin Käser
MW Monika Wälti
MG Michael Grotzer
PV Priska Vonbach
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The sample size estimation was done in collaboration with the Clinical Trial Unit of the University of Basel, Switzerland. An a priori error rate of 20% for the control study arm was assumed based on the results of previous research estimating a 26.5% error rate for dose calculation using a pocket calculator.19 A 50% overall error reduction at a significance level of 5% with >80% power resulted in a total of 600 items that need to be rated. We aimed to test the two arms for the confirmatory analysis with six items per arm, which resulted in an estimated sample size of 50 participants (600 items/12 items per participant=50 participants) (online supplemental file 3). Adding an equal number of items for the exploratory arm, the resulting total number of items that need to be rated was 900, which corresponds to 18 items per participant.

bmjpo-2022-001726supp003.pdf

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