Psychometric validation of the informed consent assessment scale using item response theory and factor analysis.

Objectives: Informed consent is a central ethical and legal practice in medicine, yet communication skills specific to this task are under-assessed in undergraduate medical education. This study aimed to develop and validate the informed consent assessment scale (ICAS), a tool designed to evaluate communication competencies essential for delivering informed consent. Methods: This psychometric validation study was conducted over three academic years (2021-2023) and included 456 fifth-year medical students who completed a 10-min OSCE station on obtaining consent for right colectomy. The ICAS was developed through expert consensus using a structured focus group and qualitative assessment of content validity. Response process evidence was collected by querying assessors about their decision-making during scoring. Internal structure was examined using the exploratory factor analysis (EFA) with tetrachoric correlations, as well as the item response theory (IRT; Rasch and 2-parameter logistic (2PL) models). Reliability was assessed using Cronbach's alpha, McDonald's omega, and IRT-derived conditional reliability. Concurrent validity was evaluated through correlations with faculty and standardized-patient communication scores. Results: Parallel analysis supported a one-factor solution. The scale demonstrated essential unidimensionality (UniCo = 0.903, ECV = 0.807, and MIREAL = 0.235) and good model fit (RMSEA = 0.032, CFI = 0.966, and WRMR = 0.039). Reliability was high (McDonald's ω = 0.841 and Cronbach's α = 0.837). Q3 analysis indicated no local item dependence (mean Q3 = -0.037 and SD = 0.100). Item discrimination parameters in the 2PL model varied across items, enabling differentiation of student performance. ICAS scores showed strong correlations with global examiner ratings and moderate correlations with broader communication scales, supporting concurrent validity. Conclusion and practice implications: The ICAS is a valid and reliable instrument for assessing communication skills specific to informed consent. Its application in objective structured clinical examinations (OSCEs) provides actionable feedback for learners and supports curriculum efforts to strengthen ethically competent clinical communication.