Sample size calculations for the development of biosimilar products

Seung Ho Kang, Yongjo Kim

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


The most widely used design for a Phase III comparative study for demonstrating the biosimilarity between a biosimilar product and a renovator biological product is the equivalence trial, whose aim is to show that the difference between two population means of a primary endpoint is less than a prespecified equivalence margin. A well-known sample size formula for the equivalence trial is given by n1 = kn2 n2 = (zα + zβ/2)2 ω2 (δ |μT - μR|)2 (1 + 1k). Since this formula is obtained based on the approximate power rather than the exact power, we investigate in this article the accuracy of the sample size formula. We conclude that the sample size formula is very conservative. Specifically, we show that the exact power based on the sample size calculated from the formula to have power is actually under some conditions. Therefore, the use of the sample size formula may cause a huge extra cost to biotechnology companies. We propose that the sample size should be calculated based on the exact power precisely and numerically. The R code to calculate the sample size numerically is provided in this article.

Original languageEnglish
Pages (from-to)1215-1224
Number of pages10
JournalJournal of Biopharmaceutical Statistics
Issue number6
Publication statusPublished - 2014 Nov 2

Bibliographical note

Publisher Copyright:
Copyright © 2014 Taylor & Francis Group, LLC.

All Science Journal Classification (ASJC) codes

  • Statistics and Probability
  • Pharmacology
  • Pharmacology (medical)


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