Measurement equivalence of the self-care of chronic illness inventory across time: longitudinal structural equation models

The Self-Care of Chronic Illness Inventory (SC-CII) is a theoretically grounded instrument comprising three scales measuring self-care maintenance, monitoring and management behaviors in adults with chronic illnesses. Although its validity and reliability have been demonstrated in cross-sectional studies, the stability of its psychometric properties over time has not been examined. This study aimed to test the longitudinal measurement equivalence of the three SC-CII Scales.

Longitudinal measurement equivalence was assessed over a 12-month period using a Confirmatory Factor Analysis (CFA) approach. Patients aged 65 or older with multiple chronic conditions (MCCs) were enrolled. Four increasingly restrictive level of invariance were tested: configural, metric, scalar and strict invariance at the first and second-order level.

Participants (N = 630) had a mean age of 77 years, were mostly female. For the Self-Care Maintenance scale, full metric invariance and partial scalar and strict invariance were achieved at both first- and second-order levels. For the Self-Care Monitoring scale, full metric and scalar invariance, and partial strict invariance were established. For the Self-Care Management scale, full metric, full scalar (first-order), partial scalar (second-order) and partial strict (first- and second-order) were achieved.

The SC-CII proved to be longitudinally stable, confirming its suitability for repeated assessments of self-care. The SC-CII can be confidently used by nurses to monitor self-care behaviors and evaluate changes during the disease trajectory, supporting the development of tailored interventions. This study demonstrated the SCCII's temporal equivalence, strengthening its use in clinical and research settings.