Psychometric Properties of the PDRQ-9 in Cancer Patients: Patient-Doctor Relationship Questionnaire

Background: The patient-doctor relationship is an important concept in health care. The aim of this study was to evaluate the psychometric properties, convergent validity, and factorial invariance of the Patient-Doctor Relationship Questionnaire (PDRQ-9). Method: Confirmatory factor analysis was conducted to explore the scale's dimensionality and test for strong measurement invariance across sex, age, and tumor site in a prospective, multicenter cohort of 560 patients who completed the PDRQ-9, Health-related Quality of Life Questionnaire (EORTC-QLQC30), and Brief Symptom Inventory (BSI) scales. Results: The data supported a unidimensional structure. Thresholds and factor loadings could be constrained to be invariant across sex, age, and tumor site, indicating strong measurement invariance. Scores derived from the unidimensional structure exhibited satisfactory degrees of reliability and determinacy. Evidence of convergent validity was supported by modest positive correlations with functional (p<.001) and global quality-of-life (p<.001) and negative correlations with psychological distress (p<.001). Low satisfaction with the oncologist was associated with anxiety (p=.006), and depression (p=.004). Conclusions: The PDRQ-9 is a suitable, valid instrument for assessing the quality of patient-doctor relationships in cancer patients.