Applying MTMM validity approach to differentiate between pain and discomfort measurements in patients with advanced cancer

The multi-trait-multi-method matrix (MTMM) is a robust method for assessing scale validity, offering a structured approach to evaluating convergent and discriminant validity by examining multiple traits measured through multiple methods. The rationale for this study stemmed from the need to distinguish between closely related constructs: pain, discomfort, and happiness in patients with advanced cancer, where accurate measurement is critical for effective symptom management. The objective was to assess the validity of these measurements using MTMM, ensuring that each construct was distinct yet reliably captured across different assessment tools. The methodology employed a cross-sectional descriptive design involving 100 patients with advanced cancer. Participants completed six questionnaires: two pain scales (numeric and non-verbal), two discomfort scales (scale and questionnaire), and two happiness measures (scale and questionnaire). The mean pain scores were 6.7 ± 2.4 (numeric scale) and 5.2 ± 2.6 (non-verbal scale), while discomfort scores were 26.6 ± 6.2 (scale) and 26.9 ± 8.0 (questionnaire). Happiness scores were 3.6 ± 1.2 (scale) and 3.2 ± 1.1 (questionnaire). Key findings revealed strong validity diagonals (r = 0.66 to r = 0.89), supporting convergent validity, while correlations between different constructs using rating scales (r = -.29 to r = .77) and hetero-trait–hetero-method coefficients (r = -.31 to r = .79) provided evidence for discriminant validity. The findings confirm MTMM as a gold-standard method in the measurement world for distinguishing between pain and discomfort in patients with advanced stages, reinforcing its utility in clinical research where precise construct differentiation is essential.