This file implements the FIS method proposed by Xing et al. and demonstrates its usage. Source: Xing Xing, Aiwen Xing, Kannan Natarajan, Haitao Chu, Lifeng Lin, Jiayi Tong, An alternative method for assessing the fragility of survival analysis results: a proof-of-concept study based on the log-rank test, American Journal of Epidemiology, Volume 195, Issue 4, April 2026, Pages 1175–1181, https://doi.org/10.1093/aje/kwaf229