The authors describe a method for the quantitative study of anchoring effects in estimation tasks. A calibration group provides estimates of a set of uncertain quantities. Subjects in the anchored condition first judge whether a specified number (the anchor) is higher or lower than the true value before estimating each quantity. The anchors are set at predetermined percentiles of the distribution of estimates in the calibration group (15th and 85th percentiles in this study). This procedure permits the transformation of anchored estimates into percentiles in the calibration group, allows pooling of results across problems, and provides a natural measure of the size of the effect. The authors illustrate the method by a demonstration that the initial judgment of the anchor is susceptible to an anchoring-like bias and by an analysis of the relation between anchoring and subjective confidence.

This study reports on experiments that examine anchoring in single referendum questions in contingent valuation surveys on willingness to pay for public goods, and on objective estimation. Strong anchoring effects are found that lead to systematically higher estimated mean responses from YesrNo referendum responses than from open-ended responses. This response pattern is similar for contingent valuation questions and for objective estimation questions. The paper concludes that psychometric anchoring effects, rather than incentive effects, are the likely cause of results commonly found in contingent valuation studies, and that the currently popular single referendum elicitation format is highly vulnerable to anchoring. q 1998 Elsevier Science B.V.

In the contingent valuation method for the valuation of public goods, survey respondents are asked to indicate the amount they are willing to pay (WTP) for the provision of a good. We contrast economic and psychological analyses of WTP and describe a study in which respondents indicated their WTP to prevent or to remedy threats to public health or to the environment, attributed either to human or to natural causes. WTP was significantly higher when the cause of a harm was human, though the effect was not large. The means of WTP for 16 issues were highly correlated with the means of other measures of attitude, including a simple rating of the importance of the threat. The responses are better described as expressions of attitudes than as indications of economic value, contrary to the assumptions of the contingent valuation method.

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