Assessing measurement invariance of a health-related quality-of-life questionnaire in radiotherapy patients

Objective: If the assumption of measurement invariance is not tested, we cannot be sure whether differences observed are due to true differences in health-related quality-of-life (HRQoL), or are measurement artifacts. We aim to investigate this assumption in a sample of heterogeneous cancer patients, focusing on whether age, sex, previous treatment for cancer, and information regarding treatment preferences result in biased HRQoL scores. Methods: 155 cancer patients who were about to begin their first session of radiotherapy were included. HRQoL was measured using the EORTC QLQ-C30. Structural equation modeling was applied to assess whether there was a violation of the assumption of invariance. Results: A satisfactory single construct (Functioning HRQoL) measurement model was found and two violations of invariance were identified. Irrespective of patients’ Functioning HRQoL, older patients reported worse physical functioning and patients who had received treatment prior to radiotherapy reported worse emotional functioning than we would otherwise expect. Conclusions: In the present study, accounting for measurement bias lead to a substantial improvement in the overall fit of the model. By ignoring the bias, we would have concluded that the model fit was unsatisfactory. The findings underline the importance of investigating measurement invariance in scales designed for heterogeneous samples

Assessment of physician competency in patient education: Reliability and validity of a model-based instrument

OBJECTIVE: Establish the inter-rater reliability and the concept, convergent and construct validity of an instrument for assessing the competency of physicians in patient education. METHODS: Three raters assessed the quality of patient education in 30 outpatient consultations with the CELI instrument. This instrument is based on a goal-directed model of patient education and assesses distinctive skills for patient education categorized in four subcompetencies. The inter-rater reliability was calculated. The concept validity was explored by factor analysis. The convergent validity was established by a comparison with two measures of patient-centred behaviour. The construct validity was explored by relating the subcompetencies with physician gender and patient satisfaction. RESULTS: The inter-rater reliability for the subcompetencies varied between 0.65 and 0.91. The factor analysis distinguished the four subcompetencies. All subcompetencies correlated with the measures of patient-centred behaviour. Female physicians performed better than male physicians on three subcompetencies. Positive correlations were found for three subcompetencies and patient satisfaction. CONCLUSION: The CELI instrument appears to be a reliable and valid instrument. However, further research is needed to establish the generalizability and construct validity. PRACTICE IMPLICATION: The CELI instrument is a useful tool for assessment and feedback in medical education since it assesses the performance of distinctive skills