A cohort study for the development and validation of a reflective inventory to quantify diagnostic reasoning skills in optometry practice

Background: Diagnostic reasoning is an essential skill for optometry practice and a vital part of the curriculum for optometry trainees but there is limited understanding of how diagnostic reasoning is performed in optometry or how this skill is best developed. A validated and reliable self-reflective inventory for diagnostic reasoning in optometry, would enable trainees and registered practitioners to benchmark their diagnostic reasoning skills, identify areas of strength and areas for improvement. Methods: A 41 item self-reflective inventory, the Diagnostic Thinking Inventory, used extensively in the medical field was adapted for use in optometry and called the Diagnostic Thinking Inventory for Optometry (DTI-O). The inventory measures two subdomains of diagnostic reasoning, flexibility in thinking and structured memory. Context based changes were made to the original inventory and assessed for face and content validity by a panel of experts. The inventory was administered to two groups, experienced (qualified) optometrists and second-year optometry students to establish validity and reliability of the self-reflective tool in optometry. Results: Exploratory Factor Analysis uncovered 13 domain specific items were measuring a single construct, diagnostic reasoning. One misfitting item was removed following Rasch analysis. Two unidimensional subdomains were confirmed in the remaining 12 items: Flexibility in Thinking (χ2 = 12.98, P = 0.37) and Structured Memory (χ2 = 8.74, P = 0.72). The ‘Diagnostic Thinking Inventory for Optometry Short’ (DTI-OS) tool was formed from these items with the total and subdomain scores exhibiting strong internal reliability; Total score Cα = 0.92. External reliability was established by test-retest methodology (ICC 0.92, 95% CI 0.83–0.96, P <.001) and stacked Rasch analysis (one-way ANOVA, F = 0.07, P = 0.80). Qualified optometrists scored significantly higher (P <.001) than students, demonstrating construct validity. Conclusion: This study showed that the DTI-O and DTI-OS are valid and reliable self-reflective inventories to quantify diagnostic reasoning ability in optometry. With no other validated tool to measure this metacognitive skill underpinning diagnostic reasoning a self-reflective inventory could support the development of diagnostic reasoning in practitioners and guide curriculum design in optometry education.