New Zealand Statistical Association 2024 Conference

Alain C. Vandal

The University of Auckland-Waipapa Taumata Rau/Te Whatu Ora Counties Manukau

Reporting randomised factorial trial results: the Topical Analgesia Post-Haemorrhoidectomy trial

This is joint work with James Jin, Weisi Xia, Runzhe Gao, Maree Weston, Lincoln Israel, Andrew Connolly, Primal Singh, Darren Svirskis, Andrew Hill

A randomised factorial trial is usually designed to detect the smallest clinically meaningful difference for all interventions, absent interaction. When a negative interaction is apparent without a sufficient sample size to test for it, the question arises as to how to best report the results, given the constraints of the statistical analysis plan (SAP). We present the rationale and decisions made in this regard when reporting the results from the Topical Analgesia Post-Haemorrhoidectomy randomised factorial trial, in which a significant difference between a metronidazole+lidocaine and a metronidazole+lidocaine+diltiazem formulation injected unexpected variability in the primary outcome, a pain visual analogue scale measured on the fourth day post-operation. While the SAP dictated the reporting of the main effects only, appropriate translation to clinical practice required separate reporting of the four arms. We describe the trial’s design, longitudinal data collection process, blind review, main analysis, and describe how we dealt with this issue.