A Review of the Sample Size Calculations of Randomised Controlled Trials Funded by One of the Leading Funders in the UK

• Activity Number: 328 - New Guidance on Specifying the Target Difference (Effect Size) for a Randomised Controlled Trial
• Type: Topic Contributed
• Date/Time: Tuesday, August 1, 2017 : 10:30 AM to 12:20 PM
• Sponsor: Biopharmaceutical Section
• Author(s): Steven Julious* and Jo Rothwell
• Companies: University of Sheffield and University of Sheffield
• Keywords: Sample size ; Effect size ; Study design ; RCT ; Target Difference

Abstract

The target difference, or "effect size", is an important component of a sample size calculation as the calculations are extremely sensitive to assumptions as to what the effect size will be. A review of 117 randomised trials in the UK funded by the NIHR Health Technology Assessment funding body found that that over 50% of randomised controlled trials report that they had used a previous study (such as a pilot trial) or previous research (such as a systematic review or meta analysis) to estimate their target effect size.

The presentation will show the results of the review. It will show how the effect size can be influenced by the method used to quantify it. It will also highlight the factors which influence the use of the different methods. The estimation of the effect size can have consequent effects on the power of the study. The most common method for elicitation can vary depending on clinical area, which will be covered in more detail.

The results will then be extended to discuss the issues with the different methods particularly when empirical results are used. For example, using an effect size previously observed to design a new study can lead to an over estimation.

Please provide feedback on the guidance document we will be presenting via survey https://oxford.onlinesurveys.ac.uk/delta2-guidance-jsm