Development and Psychometric Validation of a Comprehensive Questionnaire to Assess Oncologists' Knowledge of Chemotherapy-Drug Interaction.

Chemotherapy-drug interactions (CDIs) pose significant challenges in oncology, affecting treatment efficacy and patient safety. Despite their importance, there is a lack of validated tools to assess oncologists' knowledge of CDIs. This study aimed to develop and validate a comprehensive questionnaire to address this gap and ensure the reliability and validity of the instrument. A cross-sectional study was conducted among 135 oncologists from various clinical roles in Iraq. The questionnaire included 46 general knowledge and 26 specific knowledge items, developed based on literature and expert consultation. Psychometric validation involved exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) to assess structural validity. Reliability was evaluated through Cronbach's alpha, composite reliability (CR), and test-retest reliability using the intraclass correlation coefficient (ICC). Item Response Theory (IRT) analysis was applied to evaluate item-level performance. The EFA and CFA identified six distinct domains in the general knowledge section, with strong factor loadings for most items. Items addressing definitions, classifications, and risk factors demonstrated high loadings (e.g., "Severe chemotherapy-drug interactions often necessitate aggressive monitoring," EFA: 0.73, CFA: 0.78). Specific knowledge items also exhibited robust psychometric properties, with high discrimination indices (a > 1.5) and low guessing parameters. Reliability analysis indicated excellent internal consistency (Cronbach's alpha > 0.8) and stability over time (ICC > 0.75). The questionnaire effectively differentiated respondents based on their knowledge levels and demonstrated good model fit (CFI: 0.93, RMSEA: 0.06). This study developed and validated a reliable and robust questionnaire to assess oncologists' knowledge of CDIs. The tool provides a standardized method for evaluating CDI knowledge, addressing a critical gap in oncology practice. Future research should focus on applying this questionnaire in diverse contexts and updating it to reflect advancements in clinical guidelines and drug interaction knowledge.