Abstract
BACKGROUND: This study comprehensively examined the psychometric properties of the Brief Mishel Uncertainty in Illness Scale for patients (MUIS-P) managing advanced cancer and their caregivers (MUIS-Cg). METHODS: The MUIS-P and MUIS-Cg scales were developed based on the Mishel Uncertainty in Illness Scale-Adult. We conducted a secondary analysis to test the acceptability, factor structure, reliability, and validity of the brief uncertainty scales for patients with advanced cancer (N = 484) and their caregivers (N = 484) using data from a randomized clinical trial. RESULTS: The 9-item MUIS-P and MUIS-Cg show goodness of fit for a two-factor structure (unpredictability and ambiguity) with adequate to acceptable internal consistency (Cronbach's alpha 0.66-0.78 for patients and 0.70-0.72 for caregivers and McDonald's omega 0.72-0.84 for patients and 0.76-0.79 for caregivers). The MUIS-P and MUIS-Cg scores correlated with negative appraisals of illness/caregiving, hopelessness, and avoidant coping, demonstrating convergent validity. The discriminant validity of the MUIS-P and MUIS-Cg was evidenced by their significant correlations with self-efficacy and active coping. The baseline MUIS-P and MUIS-Cg scores were significantly associated with quality of life, hopelessness, depression, distress, and avoidant coping at the 3-month follow-up, indicating their strong predictive validity. CONCLUSION: This study comprehensively evaluated the psychometric properties of the MUIS-P and MUIS-Cg, laying a foundation for their use in research and clinical practice among patients and caregivers managing demanding symptoms and care.