The Intention of Inhaled Medication Adherence Scale (IMAS): The Development of a New Instrument for Assessing Inhaled Medication Adherence Among Patients with Chronic Obstructive Pulmonary Disease (COPD) Using Theory of Planned Behavior

Purpose: Inhaled medication adherence is an important issue for patients with chronic obstructive pulmonary disease (COPD) because adhering to inhaled medications could substantially improve their health. However, patients with COPD may not be always adhere to the prescribed inhaled medications. Therefore, understanding the underlying reasons for patients with COPD adhering to inhaled medications is important. The present study used Theory of Planned Behavior (TPB) as a theoretical framework to develop the Intention of Inhaled Medication Adherence Scale (IMAS) and assess its psychometric properties. Patients and Methods: After reviewing papers using the TPB to design psychometric scales and the TPB scale development guidelines, 28 items were generated for expert evaluation. Eight experts reported that the 28 items all had good content validity (content validity index ranged from 0.88 to 1.00 at item-level; and from 0.981 to 0.987 at scale-level) comprising four factors. Following initial development, 235 patients with COPD (mean age 73.12 years; 93.6% males) completed the IMAS via interview with a respiratory therapist and a research assistant. The four-factor structure of the IMAS was evaluated using confirmatory factor analysis (CFA). Results: Nine IMAS items were removed because of low factor loadings or offending estimates. The 19-item IMAS was confirmed as having a four-factor structure supported by the CFA results (comparative fit index=1.00; Tucker-Lewis index=1.00; root mean square error of approximation=0.00; standardized root mean square residual=0.06). Conclusion: The 19-item IMAS had satisfactory psychometric properties in construct validity. The 19-item IMAS is an instrument that could help healthcare providers understand potential factors associated with adherence to inhaled medications among people with COPD.