Deriving preliminary criterion-anchored cut-off scores for nurse-patient mutuality: A receiver operating characteristic analysis of the Nurse-Patient Mutuality in Chronic Illness Scale.

Background: Nurse-patient mutuality is a relational process associated with self-care behaviours in chronic illness. Although the Nurse-Patient Mutuality in Chronic Illness Scale (NPM-CI) has demonstrated sound psychometric properties, the absence of criterion-anchored reference points limits the interpretation of its scores across samples and settings. Objective: To derive preliminary, sample-dependent, criterion-anchored cut-off values for the NPM-CI using a prespecified threshold of self-care management as an external behavioral criterion and to examine their discriminatory performance. Methods: This observational cross-sectional study represents a secondary analysis of data from a multicentre study conducted in five healthcare centres in Italy. The analytic sample comprised 90 adults with chronic illnesses who had been recruited as the patient members of nurse-patient dyads in the source study. Only patient-reported NPM-CI and Self-Care of Chronic Illness Inventory (SC-CII) data were included; nurse-reported data were not analyzed. Self-care management was dichotomized using the established threshold of ≥70/100 to indicate adequate self-care. Receiver operating characteristic (ROC) curve analyses were performed for each NPM-CI domain. Discriminatory performance was evaluated using the area under the curve (AUC), and sample-specific thresholds were derived using the Youden Index. Pairwise comparisons of AUCs were conducted to assess differences between domains. Results: All three NPM-CI domains showed statistically significant but limited discriminatory performance in distinguishing participants who met versus did not meet the prespecified SC-CII self-care management criterion (AUC range: 0.657-0.681; p < .01). Domain-specific cut-off values were derived using the Youden Index. Although sensitivity and specificity varied across domains at their respective Youden-index thresholds, discriminatory performance did not differ significantly between domains, as indicated by pairwise comparisons of the AUCs. Conclusions: Anchoring mutuality scores to a behavioral self-care criterion enables the derivation of empirically informed thresholds that improve the interpretability of NPM-CI scores. These preliminary, sample-dependent thresholds may serve as exploratory reference points for interpreting mutuality scores in relation to self-care management. Validation in larger independent samples is required before considering any clinical application.