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  • Poster presentation
  • Open Access

Interim sample size re-estimation in the IIVOP trial

  • 1,
  • 2 and
  • 1, 3
Trials201516 (Suppl 2) :P128

  • Published:


  • Public Health
  • Healthy Volunteer
  • Primary Endpoint
  • Sample Size Calculation
  • Interim Analysis

The IIVOP trial is a cross-over trial which examines the effect of the drug ivabridine in reducing pain in an enriched healthy volunteer pain model. The trial was designed based on very limited information, and as such an interim analysis was built into the design to allow the re-estimation of the sample size requirements based on updated trial parameters.

The blinded data will be used to assess the assumptions regarding the variability of the primary endpoint. If appropriate and feasible the sample size may be increased to ensure that the study is not under-powered due to incorrect assumptions. In order to control for biases, the trial will not terminate early even if the interim sample size calculations suggests that enough patients have already been enrolled to reach the desired power.

The steps of the interim sample size re-calculation, including decisions made and results, will be presented.

Authors’ Affiliations

Cambridge Clinical Trials Unit, University of Cambridge, Cambridge, UK
Division of Anaesthesia, University of Cambridge, Cambridge, UK
MRC Biostatistics Unit, Cambridge, UK


© Dawson et al. 2015

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.


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