Sample Size Calculation Tools R package ssutil version 1.0.0 Functions for sample size estimation and simulation in clinical trials. Includes methods for selecting the best group using the Indifference-zone approach, as well as designs for non-inferiority, equivalence, and negative binomial models. For the sample size calculation for non-inferiority of vaccines, the approach is based on Fleming, Powers, and Huang (2021) <doi:10.1177/1740774520988244>. The Indifference-zone approach is based on Sobel and Huyett (1957) <doi:10.1002/j.1538-7305.1957.tb02411.x> and Bechhofer, Santner, and Goldsman (1995, ISBN:978-0-471-57427-9). Software Depends: R (>= 4.1) Imports: stats, stringr, broom, MASS, gsDesign, mvtnorm, tibble Suggests: knitr, rmarkdown, spelling, testthat (>= 3.0.0) John J. Aponte <john.j.aponte@gmail.com> Comprehensive R Archive Network (CRAN) John J. Aponte [aut, cre] (ORCID: <https://orcid.org/0000-0002-3014-3673>), Chris Gast [ctb] AGPL (>= 3) 2025-06-12 application/tgz https://CRAN.R-project.org/package=ssutil doi:10.32614/CRAN.package.ssutil en-US