Evaluation of the psychometric properties of the Early Morning Symptoms of COPD Instrument (EMSCI)

BACKGROUND: Early morning respiratory symptoms impact quality of life and are often the most troublesome for patients with COPD. Reduction in symptoms and their impact are important treatment outcomes for COPD. The Early Morning Symptoms of COPD Instrument (EMSCI) is a daily diary designed to collect patients’ report of the occurrence, severity, and impact of morning COPD symptoms. METHODS: To assess the psychometric properties of the EMSCI, a split-half sample of data from a COPD clinical trial where participants completed the EMSCI daily was used for conducting descriptive statistics, factor analyses, and Rasch model analyses to examine item performance and inform scoring. Once the final scoring algorithm was determined, data from the second split-half sample were used to examine the properties of the EMSCI. Test–retest reliability was assessed using intraclass correlation coefficient (ICC). Correlations with other study assessments were used to evaluate convergent and known-groups validity. RESULTS: Data from 1,663 patients with COPD aged 40–93 years were analyzed. Factor analysis and Rasch analysis confirmed a one-factor structure for the 6 individual symptom items. Item analyses supported the generation of 4 scores. All scores demonstrated good test–retest reliability: 6-item symptom severity (ICC, 0.84); overall morning symptom severity (ICC, 0.84); activity limitation (ICC, 0.85); and rescue medication (ICC, 0.62). Significant correlations between EMSCI scores, St George’s Respiratory Questionnaire scores, and EXAcerbations of Chronic pulmonary disease Tool (EXACT)-Respiratory Symptoms scores supported the tool’s convergent validity. Significant differences (p<0.0001) in all EMSCI domain scores were found between known-groups based on median split St George’s Respiratory Questionnaire and EXACT-Respiratory Symptoms scores. CONCLUSION: The EMSCI consists of 4 scores: 6-item symptom severity, overall symptom severity, activity limitation, and rescue medication. The EMSCI is a reliable and valid instrument for evaluating patients’ experience of early morning COPD symptoms.