Quality of life in low-income patients with metastatic prostate cancer: Divergent and convergent validity of three instruments

Few studies have evaluated Quality Of Life (QOL) among low-income patients with cancer. Information is needed about the feasibility and psychometric c haracteristics of QOL instruments in these populations. The purpose of this study was to examine the convergent and discriminant relationships between scales of three QOL instruments: European Organization for Research and Tr eatment of Cancer Quality of Life Questionnaire (EORTC), Functional Assessm ent of Cancer Therapy - General (FACT), and Quality of Life Index (QLI). Pa rticipants included 110 men with metastatic prostate cancer of whom 94% wer e low income and 62% were African-American. Interviewers administered the q uestionnaires. Cronbach alpha internal consistency reliabilities were 0.57 to 0.90 for the EORTC, 0.65 to 0.86 for the FACT, and 0.63 for the QLI. Con vergent validity was supported for the EORTC and FACT scales measuring emot ional, physical, and role/functional dimensions (r = 0.54 to 0.72), but not on scales measuring social function (r = 0.12). Divergent validity was sup ported between dissimilar scales (r = 0.14 to 0.38). Analysis with receiver operating characteristics curves provided empirical support for the EORTC and FACT as multidimensional measures. These findings suggest that, even in busy clinical settings with low literacy patients, interviewer-administere d EORTC and FACT QOL instruments can provide valid and reliable information .