Is expressed WTP consistent with welfare economics? A response from 73 cognitive interviews

Contingent valuation is based on the hypothesis that people are able to estimate an improvement of their well-being in terms of income reduction and that the value they give can be assimilated to a price. To test this assumption we ran 73 in-depth interviews with persons suffering from air pollution. Most of the persons express a lump sum. Only 12 % of the persons with a positive WTP are able to construct a value in terms of opportunity costs and increase in quality of life. It is easier to express a lump sum than to try to build a "price" because the cognitive exercise is simpler.