Heterogeneity in item content of quality of life assessments used in depression research

Purpose: Quality of life (QOL) refers broadly to the assessment of well-being, life satisfaction, and psychosocial functioning. Depression, a leading cause of disability worldwide, is associated with lower QOL. However, QOL literature presents varying definitions of the concept with no consensus on the best definition or conceptual model. As measurement-based care initiatives and patient-reported outcomes have become a standard for quality care, the number of QOL assessments has increased. It is unclear how much heterogeneity there is in the measurement of QOL across instruments. The aim of the present study was to quantitatively and qualitatively describe item content overlap among QOL measures commonly used in depression research. Methods: We identified 10 QOL measures from a recent meta-analysis and quantified the degree of item content overlap by calculating the Jaccard Indices across measures, a similarity coefficient for binary data. We coded overlap using two approaches: one defined content overlap as involving any similarly worded items (e.g., “down” and “blue”), and a second defined content overlap as using exactly the same word or root (e.g., “anxiety” and “anxious”). We also employed a mixed methods approach to code all items into broader themes. Results: Both approaches yielded low levels of item content overlap (M1=0.14, SD1=0.12; M2=0.07, SD2=0.08), reflecting substantial heterogeneity among common measures of QOL used in depression. Conclusion: Popular measures of QOL assess very different content, raising the possibility that outcomes may not be reproducible across scales. Future work should explore the relations among content assessed in measures of QOL.