Assessing Dietary Supplement Knowledge in Registered Dietitians: Development and Content Validation of the DSKAT-RD

Introduction: Registered dietitians (RDs) are frequently asked to provide guidance and expertise on dietary supplements; however, few assessment tools are available to objectively evaluate their knowledge in this area. A standardized instrument may help identify educational gaps and support the development of supplement-related competencies within dietetics education and practice. Methods: The 25-item Dietary Supplement Knowledge Assessment Tool for Registered Dietitians (DSKAT-RD) was developed to assess key areas of dietary supplement knowledge, including safety, efficacy, regulation, quality, and evidence-based research. Twelve subject-matter experts independently rated the relevance of each item on a 4-point scale. Item-Level Content Validity Index (I-CVI) values were calculated, with ratings of 3 or 4 considered content valid and ≥0.78 considered acceptable. Quantitative ratings and qualitative feedback guided revisions for clarity, accuracy, relevance, and response-option quality. Revised items were reviewed by a 3-member expert subgroup until consensus was reached. Results: Expert review demonstrated high content validity for the DSKAT-RD. Item-level Content Validity Index (I-CVI) values ranged from 0.75 to 1.00, with 24 of 25 items (96%) meeting the predefined acceptability criterion of ≥0.78. Nineteen items (76%) achieved an I-CVI of 1.00, and the Scale-Level Content Validity Index using the average method (S-CVI/Ave) was 0.97. Six items underwent additional review and revision based on quantitative ratings and qualitative expert feedback related to wording, response options, scientific or regulatory accuracy, and content alignment. Following secondary review by three subject-matter experts, all 25 items were retained in the final instrument. Conclusions: The DSKAT-RD demonstrated strong evidence of content validity and provides a structured method for assessing dietary supplement knowledge among RDs.