In this chapter, we discuss sample size determination in clinical trials with implementation in R. We begin with a review of the prerequisites for sample size determination in Section 7.1. We then present sample size calculations for the comparison of two treatment groups for continuous endpoints in Section 7.2 followed by the two treatment comparison for proportions in Section 7.3. In

for clinical design group sequential trials including sample size calculation and stopping boundaries. Design and sample size calculation for trials with longitudinal data is discussed in Section 7.6. In Section 7.7, we discuss an atypical situation in sample size calculation where percent change and coefficient of variation are known and end the chapter with concluding remarks in Section 7.8.