Domains, constructs and the development of the breathing problems questionnaire.

Health-related quality of life (QoL) questionnaires are commonly developed as content valid instruments with conventionally defined domain subscales. We contrasted content valid domain subscales with construct valid construct subscales and developed a 13-domain QoL questionnaire, the Breathing Problems Questionnaire (BPQ), for patients with chronic bronchitis. In a series of studies, we examined the constructs relevant to COPD patients' experience of health. First, we provided psychometric evidence that items in the BPQ form two distinct groups: functional problems and negative evaluations. Second, we showed that problems were significantly more correlated with morbidity whereas negative evaluations were significantly more correlated with neuroticism. Third, we showed that negative evaluations correlated with neuroticism whereas positive evaluations (measured by the Satisfaction with Illness Scale) correlated with extraversion. Patients are more likely to make positive evaluations of their illness when they recognize that they are seriously ill. Most of the BPQ domains are subcategories of the construct of problems: both domains and construct classifications provide useful information.