Development and validation of a patient satisfaction and preference questionnaire for inhalation devices.

Introduction: The Patient Satisfaction and Preference Questionnaire (PASAPQ) is a multi-item measure of respiratory inhalation device satisfaction and preference designed to be easily understood and administered to patients with asthma and COPD. This study assessed its validity, reliability and responsiveness and explored the between-group difference in PASAPQ scores that is meaningful.

Methods: The field test version was developed using literature, focus groups and expert opinion. Item reduction followed. The assessment of the validity, reliability and responsiveness of the PASAPQ utilized data from two clinical studies comparing devices delivering the same medication, and was performed with pre-specified criteria. A minimally important difference (MID) was estimated using both anchor- and distribution-based approaches.

Results: Two factors of the PASAPQ, 'performance' and 'convenience', were consistent across studies. Missing and out-of-range data were minimal (<1%) and respondents used a full range of response options. All items correlated most highly with their hypothesized scale and all exceeded the minimum correlation criteria of 0.40. Cronbach's alfa was high (0.87-0.94), providing support for internal reliability for the PASAPQ. Correlations of the overall satisfaction item with the performance domain ranged from 0.78 to 0.91, the convenience domain ranged from 0.54 to 0.71, and the total score ranged from 0.78 to 0.90. These moderate-to-strong correlations provide substantial support for the validity of the PASAPQ domains and total score. Discriminate validity was assessed by calculating PASAPQ scores for patients' ratings of the device that they preferred compared with the other, non-preferred device. The preferred device was rated higher on all satisfaction measures, supporting the ability of the PASAPQ to discriminate between preferred and non-preferred devices. Although a difference of 3 or 4 points may be sufficient to observe a small effect difference between groups, most of the MID estimates were in the 8-10 point range.

Discussion and conclusion: Our analyses across asthma, COPD and patients with mixed respiratory disease (with features of both COPD and asthma), study designs and data sets lead us to conclude that the PASAPQ is a practical, valid, reliable and responsive instrument for measuring respiratory device satisfaction. Furthermore, a difference in satisfaction scores between treatment groups of 10 points is, conservatively, a difference that is meaningful to patients.