The concepts of sample size estimation are introduced, including when and why this might be necessary. Formulae are presented and discussed. An accompanying weblink is introduced which hosts excel sheets pre-programmed to facilitate use of the formulae. In the morning the precision-based approach to sample size estimation is introduced, whereby the numbers are selected to produce a confidence interval for the relevant estimate with a specified width. In the afternoon we progress to the more traditional power calculations that aim to give the sample required to determine a specified difference with selected power and significance levels. All terminology will be explained as it is introduced in the sessions.Sample size estimation is discussed for the following measurements:MeansProportions/ percentagesTime to event dataRatesMeasures of agreementDelegates are welcome to bring their own laptops and access to the UCL Guest network will also be provided. Everyone wishing to bring their own computer should ensure Microsoft Excel (or alternative compatible software) is installed before attending.