The framework and methods of sample size estimation for quantitative repeated measurement data in clinical research: comparison of the difference between groups at a single time point

Repeated measurement quantitative data in clinical research is versatile, allowing for the exploration of three different research questions, its diversity of statistical analysis methods and outcome indicators makes the thinking of sample size estimation specific to repeated measurement quantitative data. However, there is currently no study that introduced the thinking of sample size estimation for repeated measures of quantitative data based on the main research question, primary statistical analysis method and the definition of primary outcome indicator in statistical analysis plan. Additionally, due to the two specific parameters regarding data correlations and repeated measurement times in repeated measures design, its sample size calculation approach is more complicated than the traditional methods (e.g. method based on t-test). Therefore, the study aims to introduce the sample size calculation approach based on different statistical methods and definitions of outcome indicators to address the research question about comparing differences between groups at a single time point, and explore the differences in sample sizes calculated by various methods with different data correlations and repeated measurement times to provide valuable insights for clinical research teams.