A s a method of measuring the benefits of goods for which there are no markets, asking people directly to value public goods has many

desirable properties. Nevertheless, the beliefs about human behavior embraced by economists make them deeply suspicious of data gathered by the contingent valuation techniques. This attitude contrasts sharply with their respect for studies that use indirect valuation methods, despite the long chain of assumptions made between the data gathered by these methods and the benefits they seek to measure (Mendelsohn and Brown, 1983; Smith, 1986b). As noted, the crucial difference between the indirect and the direct methods is that indirect methods are based on actual behavior, whereas direct questioning necessarily relies on the respondents' willingness to reveal their true preferences.