Have a little faith: Measuring the impact of illness on positive and negative aspects of faith

Background The importance of faith and its associations with health are well documented. As part of the Patient Reported Outcomes Measurement Information System, items tapping positive and negative impact of illness (PII and NII) were developed across four content domains: Coping/Stress Response, Self-Concept, Social Connection/Isolation, and Meaning and Spirituality. Faith items were included within the concept of meaning and spirituality. Methods This measurement model was tested on a heterogeneous group of 509 cancer survivors. To evaluate dimensionality, we applied two bi-factor models, specifying a general factor (PII or NII) and four local factors: Coping/Stress Response, Self-Concept, Social Connection/Isolation, and Meaning and Spirituality. Results Bi-factor analysis supported sufficient unidimensionality within PII and NII item sets. The unidimensionality of both PII and NII item sets was enhanced by extraction of the faith items from the rest of the questions. Of the 10 faith items, nine demonstrated higher local than general factor loadings (range for local factor loadings = 0.402 to 0.876), suggesting utility as a separate but related 'faith' factor. The same was true for only two of the remaining 63 items across the PII and NII item sets. Conclusions Although conceptually and to a degree empirically related to Meaning and Spirituality, Faith appears to be a distinct subdomain of PII and NII, better handled by distinct assessment. A 10-item measure of the impact of illness upon faith (II-Faith) was therefore assembled.