Viewpoint: Do not resurrect the two-stage procedure

Stephen Senn*

*Corresponding author for this work

Research output: Contribution to journalArticleResearchpeer-review


In 1989, Peter Freeman published a paper that challenged a commonly accepted approach for analyzing cross-over trials, the so-called two-stage procedure. Freeman himself recommended using the Bayesian approach of Andy Grieve. The flaws Freeman exposed were serious and led many statisticians to conclude that the procedure was unacceptable. Unfortunately, more than 30 years later, one still encounters its use. This note explains, using a simple simulation, why the two-stage procedure is, indeed, as Freeman showed unacceptable and should not be used.

Original languageEnglish
Pages (from-to)808-814
Number of pages7
JournalPharmaceutical Statistics
Issue number4
Publication statusPublished - 1 Jul 2022
Externally publishedYes


  • cross-over trial
  • error inflation
  • inference
  • pretesting


Dive into the research topics of 'Viewpoint: Do not resurrect the two-stage procedure'. Together they form a unique fingerprint.

Cite this