Designing Contingent Valuation Scenarios for Environmental Health: the Case of Childhood Asthma

Objectives: We use a contingent valuation (CV) study of childhood asthma to discuss a central issue in designing CV studies of chronic illness—the need for a detailed, realistic scenario that minimizes confounding factors—and show how to address this issue. We apply our methodology to estimate households’ willingness to pay (WTP) for reductions in asthma morbidity. Methods: Using a combination of focus groups, revealed preference surveys, and epidemiological surveys, we gathered information on health status, attitudes and beliefs regarding asthma, risk-averting behaviors, perceptions of these behaviors and household socioeconomic characteristics. We used this information to design a CV survey, which we extensively tested for validity. In the survey, we elicited participants’ WTP for a hypothetical device that would reduce symptom-days by improving their asthma management; these data enabled us to estimate household WTP using a variety of econometric models. Results: Our analysis of households with children with asthma yielded the following conclusions: the scenario should address both physical asthma symptoms and the psychosocial stress of managing a chronic illness; the survey should measure household perceptions of the burden of asthma in addition to objective measures such as symptom-days; and the scenario should not involve substantial behavioral change or a new medication in order to avoid confounding of household preferences with unrelated attributes of the scenario. Our primary models estimated mean household WTP for a 50% reduction in symptom-days (and accompanying reductions in psychosocial stress) at $56.48 to $64.84 per month. Conclusions: Our methodology can be used to inform CV studies of chronic illness. Our WTP estimates can help regulatory agencies assess a wide range of policies that affect the incidence or severity of asthma.