Methodological issues in measuring subjective well-being and quality-of-life: Applications to assessment of affect in older, chronically and cognitively impaired, ethnically diverse groups using the Feeling Tone Questionnaire.

Quality of life assessment includes measurement of positive affect. Methods artifacts associated with positively and negatively worded items can manifest as negative items loading on a second factor, despite the conceptual view that the items are measuring one underlying latent construct. Negatively worded items may elicit biased responses. Additionally, item-level response bias across ethnically diverse groups may compromise group comparisons. The aim was to illustrate methodological approaches to examining method factors and measurement equivalence in an affect measure with 9 positively and 7 negatively worded items: The Feeling Tone Questionnaire (FTQ). The sample included 4,960 non-Hispanic White, 1,144 non-Hispanic Black, and 517 Hispanic community and institutional residents receiving long-term supportive services. The mean age was 82 (s.d.=11.0); 73% were female. Two thirds were cognitively impaired. Methods effects were assessed using confirmatory factor analyses (CFA), and reliability with McDonald's omega and item response theory (IRT) generated estimates. Measurement equivalence was examined using IRT-based Wald tests. Methods effects associated with negatively worded items were observed; these provided little IRT information, and as a composite evidenced lower reliability. Both 13 and 9 item positive affect scales performed well in terms of model fit, reliability, IRT information, and evidenced little differential item functioning of high magnitude or impact. Both CFA and IRT approaches provided complementary methodological information about scale performance. The 9-item affect scale based on the FTQ can be recommended as a brief quality-of-life measure among frail and cognitively impaired individuals in palliative and long-term care settings.