Development and evaluation of an interview instrument for the monetary valuation of expected and perceived health effects using rehabilitation interventions as a model

Purpose: The objective of this pilot study was to develop, test and modify an interview instrument to assess WTP for expected and perceived small to moderate health effects. To examine this objective, a comprehensive inpatient rehabilitation or day-clinic program for patients with pain or depression was used as a model. Material and method: The instrument for the structured interview was developed focusing on criteria considered as necessary and sufficient for a valid CV scenario. We then 1) examined the general comprehensibility of the WTP interview, 2) examined the feasibility of assessing the monetary value of expected and perceived health effects, 3) identified the range of monetary values for a payment scale to be used in contingent valuation (CV) studies in the target population and 4) explored the validity of the CV by examining known associations of the WTP with income. Results: 30 patients took part in the pilot study. The developed instrument for the structured interview is theoretically accurate and seems policy relevant. It was found to be comprehensible, plausible and meaningful by respondents as intended when applying it in the day-clinic and inpatient setting. The feasibility of the WTP interview to assess the monetary value of expected and perceived health effects was good with a high response rate of 93.3% ex-ante and 95.2% ex-post. The found monetary values ranged from E20 to E2.500. The range for a payment scale to be used in CV studies in the target population therefore needs to cover the range from E0 to E1.000 and more. The validity of the CV could be confirmed by the expected positive association of the ex-post WTPmax with disposable income (R-2 0.672; p < 0.002), insurance status (R-2 0.476; p < 0.034), and job qualification (R-2 0.507; p < 0.032). Conclusion: The developed questionnaire was found to be suitable for the examined population in the context of the German health care system and is valid with respect to known and expected associations with income, insurance status and job qualification. The range of monetary values is the basis for a payment scale to be used in future studies in the target population. Based on this pilot study, WTP is a promising method for assessing the value of small to moderate health effects.