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Abstract* Background Sample size determination is one of the least reported elements in the methods sections of health professions education (HPE) research. Underpowered studies miss real effects, whereas overpowered studies waste participants and resources. Guidance on sample size remains fragmented, distributed across statistical textbooks and discipline-specific papers, with no unified reference for HPE researchers. Methods Rather than proposing a universal formula, which does not exist, we organised sample-size logic by study design, reflecting how investigators plan their research. We set out a stepwise determination workflow and emphasise sourcing the assumed effect size from a pilot study or a comparable parent study. For each design we present the statistical rationale, the applicable formula or rule of thumb, a worked example grounded in HPE practice, and explicit reporting expectations. Results The designs covered include two-group comparisons of means and proportions, pre–post and repeated-measures designs, cluster-randomized educational trials, survey and questionnaire studies, Delphi and consensus studies, pilot and feasibility studies, qualitative enquiry, simulation-based education, and instrument validation. The guide concludes with reporting standards for the methods section, written to serve investigators, peer reviewers, and journal editors. Conclusions Sample size in HPE research is a design-specific judgment, not a formula-specific calculation. This guide consolidates that judgment into a practical and rigorous reference that reflects the methodological diversity of the field.
Naqvi et al. (Mon,) studied this question.