Patterns of treatment effects in subsets of patients in clinical trials

Biostatistics. 2004 Jul;5(3):465-81. doi: 10.1093/biostatistics/5.3.465.


We discuss the practice of examining patterns of treatment effects across overlapping patient subpopulations. In particular, we focus on the case in which patient subgroups are defined to contain patients having increasingly larger (or smaller) values of one particular covariate of interest, with the intent of exploring the possible interaction between treatment effect and that covariate. We formalize these subgroup approaches (STEPP: subpopulation treatment effect pattern plots) and implement them when treatment effect is defined as the difference in survival at a fixed time point between two treatment arms. The joint asymptotic distribution of the treatment effect estimates is derived, and used to construct simultaneous confidence bands around the estimates and to test the null hypothesis of no interaction. These methods are illustrated using data from a clinical trial conducted by the International Breast Cancer Study Group, which demonstrates the critical role of estrogen receptor content of the primary breast cancer for selecting appropriate adjuvant therapy. The considerations are also relevant for general subset analysis, since information from the same patients is typically used in the estimation of treatment effects within two or more subgroups of patients defined with respect to different covariates.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antineoplastic Agents, Phytogenic / therapeutic use
  • Breast Neoplasms / drug therapy
  • Clinical Trials, Phase III as Topic / methods*
  • Data Interpretation, Statistical*
  • Disease-Free Survival
  • Female
  • Humans
  • Middle Aged
  • Neoplasms, Hormone-Dependent / drug therapy
  • Randomized Controlled Trials as Topic / methods*
  • Tamoxifen / therapeutic use
  • Treatment Outcome*


  • Antineoplastic Agents, Phytogenic
  • Tamoxifen