Is Susceptibility to Homeopathic Potency a Measurable Construct? Development of an Assessment Tool by Mixed-Methods Research

Background: Susceptibility, a foundational concept in homeopathy, denotes an individual's reactive capacity that governs disease manifestation, remedy response and potency selection. Despite its central role, susceptibility has remained a qualitative construct without standardized measurement. This study aimed to conceptualize and develop a content-validated instrument to measure susceptibility to different potencies of homeopathic medicines. Methods: An exploratory sequential mixed-methods design (qual → QUAN) was employed. Conceptual domains were identified through classical literature review and expert free-listing, with item salience estimated using Smith's salience index. Face validity was assessed by four independent raters, followed by Delphi-based content validation with another five-member expert panel using average congruency percentage (ACP), content validity ratio (CVR), content validity index (CVI), including I-CVI (content validity index: item-specific) and S-CVI (content validity index: scale-specific), and kappa statistics. A pilot test by 15 postgraduate trainees (end-users) evaluated clarity and feasibility. An exploratory receiver operating characteristic (ROC) analysis was conducted to preliminarily calibrate score thresholds against expert-rated susceptibility levels (low, medium, high). Results: < 0.001), with curves closely approximating the upper-left boundary, indicating high sensitivity and specificity. Optimal cut-off points were identified, enabling empirical classification of susceptibility as low (<60.7), moderate (60.7-66.9) or high (>66.9). Conclusion: This study presents the first standardized, content-validated and pilot-tested instrument to quantify susceptibility in homeopathy. The exploratory ROC findings provide preliminary empirical thresholds for classifying susceptibility levels, supporting more consistent and objective potency selection. Further psychometric testing, including reliability and construct validity, will be reported elsewhere.