OBJECTIVES: To aid interpretation of scores on the Living with COPD scale (LCOPD; scored 0-22), COPD and Asthma Sleep Impact Scale (CASIS; scored 0-100) and COPD and Asthma Fatigue Scale (CAFS, scored 0-100). These new patient reported outcome measures, designed for use in clinical trials, have previously been shown to be reliable and valid. METHODS: Questionnaire data from UK (n=162; 46% male; mean age=69.3 years) and US (n=145; 51% male; mean age=71.7 years) surveys were analysed. Mean questionnaire scores were evaluated against clinician severity rating and by exacerbation status (US only). Effect sizes (ES) and standard errors of measurement (SEM) were used to provide a preliminary estimate of the minimal important difference (MID). RESULTS: Scores on the LCOPD and CAFS were significantly related to clinician rating of COPD severity (p<0.001). A similar trend for the CASIS was not statistically significant. Scores on all measures were also significantly higher (p<0.05), indicating greater impairment if the patient had had an exacerbation in the previous week. For the LCOPD the values for 0.3 ES, 0.5 ES and SEM were 2.0, 3.3 and 1.4 respectively. For the CASIS the figures were 7.4, 12.3 and 7.4 and for the CAFS; 7.3, 12.2 and 5.5. Therefore, these distribution-based analyses suggest that the MID is in the region of 2 for the LCOPD and 7 for the CASIS and CAFS. CONCLUSIONS: The analyses provide preliminary information on how to interpret scores on the scales. Further analyses of longitudinal data are required to confirm these findings, to assess anchor-based estimates and to allow greater precision in powering studies using these questionnaires.