Psychometric properties of an instrument for assessing the experience of patients treated with inhaled insulin: the Inhaled Insulin Treatment Questionnaire (IITQ)

BACKGROUND: Along with general measures of treatment satisfaction, treatment-specific and device-specific treatment satisfaction should be assessed in clinical trials, because these latter measures may be more strongly correlated with clinical outcomes. METHODS: Study participants were 1076 adults (type 1 = 509, type 2 = 567) in clinical trials of Technosphere Insulin(®), who completed the SF-36 health-related quality of life questionnaire and the Inhaled Insulin Treatment Questionnaire (IITQ), a new instrument assessing diabetes worries, perceptions of insulin therapy, treatment satisfaction, treatment preference, and inhaler performance. The IITQ was administered twice prior to treatment initiation in the clinical trials, 1-2 weeks apart, and several times during the trials. Inhaler performance was assessed at follow-up visits, after participants had used the device. RESULTS: IITQ subscales had acceptable reliability (alpha = 0.68-0.87, median 0.83) and test-retest correlations (intra-class correlation coefficient = 0.67-0.90, median 0.82); floor effects (0.2-2.8%) and ceiling effects (0-9.3%) were minimal. Reliabilities for inhaler performance measures were acceptable (alpha = 0.73-0.90, median 0.85); there were no floor effects (0.0%) and ceiling effects (4.9-39.0%) were moderate. There were several modest associations between IITQ scores and measures of health status. Diabetes worries were lower for participants who had better mental health (type 2) and for those with higher BMI; perceptions of insulin therapy were more favorable for participants who had better physical and mental health; treatment satisfaction was higher for patients who had lower BMI (type 2), lower A1c levels, and better physical health (type 2); treatment preference was higher for patients with lower BMI (type 2) and better mental health (type 1). CONCLUSIONS -: Preliminary findings suggest that the IITQ is a comprehensive, reliable measure of the experience of patients treated with inhaled insulin.