Do patient characteristics matter when calculating sample size for eczema clinical trials?

L Howells; S Gran; J R Chalmers; B Stuart; M Santer; L Bradshaw; D M Gaunt; M J Ridd; L A A Gerbens; P I Spuls; C Huang; N A Francis; K S Thomas

doi:10.1002/ski2.42

Do patient characteristics matter when calculating sample size for eczema clinical trials?

Skin Health Dis. 2021 May 19;1(3):e42. doi: 10.1002/ski2.42. eCollection 2021 Sep.

Authors

L Howells¹, S Gran¹, J R Chalmers¹, B Stuart², M Santer², L Bradshaw³, D M Gaunt⁴, M J Ridd⁴, L A A Gerbens⁵, P I Spuls⁵, C Huang⁶, N A Francis^{2

7}, K S Thomas¹

Affiliations

¹ Centre of Evidence Based Dermatology School of Medicine University of Nottingham King's Meadow Campus Nottingham UK.
² Primary Care Research Centre School of Primary Care Population Sciences and Medical Education University of Southampton Southampton UK.
³ Nottingham Clinical Trials Unit University of Nottingham Nottingham UK.
⁴ Bristol Medical School: Population Health Sciences University of Bristol Bristol UK.
⁵ Department of Dermatology Amsterdam Public Health Infection and Immunity Amsterdam UMC University of Amsterdam Amsterdam the Netherlands.
⁶ Hull York Medical School University of Hull Hull UK.
⁷ Division of Population Medicine Cardiff University School of Medicine Cardiff UK.

PMID: 35663143
PMCID: PMC9060078
DOI: 10.1002/ski2.42

Abstract

Background: The Patient-Oriented Eczema Measure (POEM) is the core outcome instrument recommended for measuring patient-reported atopic eczema symptoms in clinical trials. To ensure that the statistical significance of clinical trial results is meaningful, trials are often designed by specifying the target difference in the primary outcome as part of the sample size calculation. One method used to specify the target difference is a score that corresponds to a standardized effect size.

Objectives: to assess how the standardized effect size of POEM scores vary across age, gender, ethnicity and disease severity.

Methods: This study combined data from five UK-based randomized clinical trials of eczema treatments in order to assess differences in self-reported eczema symptoms (POEM) corresponding to a standardized effect size (0.5 SD of baseline POEM scores) across age, gender, ethnicity and disease severity.

Results: POEM scores corresponding to 0.5 SD_(baseline) were remarkably consistent across participants of varying ages, gender, ethnicity and disease severity from datasets of five UK trials in children (range 2.99-3.45).

Conclusions: This study provides information that can support those designing clinical trials to determine their sample size and can aid individuals interpreting trial results. Further exploration of differences in populations beyond the United Kingdom is needed.