Background and objective: Previous work has suggested that people with poor health-related quality of life (HR-QOL) as a result of asthma are willing to pay the most for successful therapy. There is also evidence that preferences are an important influence on adherence to therapy. We report a patient preference study using a discrete-choice experiment (DCE) to elicit willingness to pay (WTP) of patients with asthma in Spain, the Netherlands, and the UK.
Methods: The DCE survey included different attributes of asthma therapy (days with symptoms, days needing reliever medication, asthma attacks [none, attack that does not require doctor/emergency room {ER} visit, attack that requires doctor/ER visit], risk of adverse effects, number of preventer inhalers, and monthly out-of-pocket costs). Participants indicated which attribute combinations they preferred. The questionnaire survey included the mini Asthma Quality of Life Questionnaire (mAQLQ). The validity of the choice experiment has been supported by two pilot studies conducted in the UK. Preferences and WTP were estimated using a random effects probit model. Symptom days and asthma attack attributes were segmented by mAQLQ score.
Results: Demographic and clinical data were compared between the three country samples (UK, n = 124; Spain, n = 86; the Netherlands, n = 269). All study attributes were independently significant predictors of choice. People were willing to pay €35 per month to avoid a day with symptoms, and €109 per month (year 2005 values) to avoid experiencing asthma attacks that required emergency visits to their doctor or hospital. People with the worst HR-QOL were willing to pay the least to avoid days with symptoms and asthma attacks that required visits to their doctor/ER. This was not an income-related effect.
Conclusion: Patients who reported higher HR-QOL were willing to pay more to avoid days with symptoms and asthma attacks that required visits to their doctor/ER. Hypotheses were explored to explain this effect. It is possible that people with the least impairment of HR-QOL place the greatest value on avoiding the effects of asthma and so are most willing to alter their behavior. People with the worst HR-QOL may be exhibiting a response shift type of effect whereby their internal values are shifted down by the burden of their disease. These findings may help to illuminate why there are differences in asthma treatment adherence.