Willingness to Pay and Sensitivity to Time Framing: A Theoretical Analysis and an Application on Car Safety

Stated preference (SP) surveys attempt to obtain monetary values for non-market goods that reflect individuals’ “true” preferences. Numerous empirical studies suggest that monetary values from SP studies are sensitive to survey design and so may not reflect respondents’ true preferences. This study examines the effect of time framing on respondents’ willingness to pay (WTP) for car safety. We explore how WTP per unit risk reduction depends on the time period over which respondents pay and face reduced risk in a theoretical model and by using data from a Swedish contingent valuation survey. Our theoretical model predicts the effect to be nontrivial in many scenarios used in empirical applications. In our empirical analysis we examine the sensitivity of WTP to an annual and a monthly scenario. Our theoretical model predicts the effect from the time framing to be negligible, but the empirical estimates from the annual scenario are about 70 % higher than estimates from the monthly scenario.     

Comparison of Internet and interview survey modes when estimating willingness to pay using choice experiments

With the increasing use of the Internet as a survey mode, questions of mode effects and how potential effects influence inferences arise. Using a choice experiment combined with mixed logit estimation, willingness-to-pays (WTPs) for attributes are compared between the Internet mode and the more traditional interview survey mode. The results suggest that there are differences in WTP between the two survey models for three of four attributes. Furthermore, WTPs obtained from the interview survey are larger than the WTPs obtained from the Internet survey, suggesting potential social desirability behaviour by the interview respondents. Internet surveys involving sensitive issues may be desirable because of potential social desirability behaviour.     

Are Internet surveys an alternative to face-to-face interviews in contingent valuation?

Internet is an increasingly popular data collection mode for stated preference research in environmental economics. However, little is known about how this survey mode may influence data quality and welfare estimates. As part of a national contingent valuation (CV) survey estimating willingness to pay (WTP) for biodiversity protection plans, we assign two groups of respondents either to an Internet or face-to-face (in-home) interview mode. Our design aims to better isolate measurement effects from sample composition effects by drawing both samples from the same sample frame. We find little evidence of social desirability bias in the interview setting or satisficing (shortcutting the response process) in the Internet survey. The share of “don't knows”, zeros and protest responses to the WTP question with a payment card is very similar between modes and equality of mean WTP cannot be rejected. Results are fairly encouraging for the use of Internet in CV as stated preferences do not seem to be significantly different or biased compared to face-to-face interviews.     

Ordering effects in contingent valuation surveys

This paper focuses on ordering effects in CVM surveys; how the expressed value of a particular good valued in a sequence of several goods depends on where in the sequence the good is valued. We use data from a Norwegian CVM survey focusing on WTP for a 50% reduction in air pollution from car traffic to test for the existence of ordering effects and to apply a test for internal consistency. We found considerable and significant ordering effects in our data, but were not able to reject the hypothesis of internal consistency. Based on our survey, we argue that ordering effects may be a result of rational choice. These effects are problematic if a sequential valuation procedure is applied to a simultaneous problem, and/or the respondents are given imperfect information about the decision problem.     

A Meta-study Investigating the Sources of Protest Behaviour in Stated Preference Surveys

It is a well-known empirical finding that some percentage of respondents participating in Stated Preference surveys will not give responses that reflect their true preferences. One reason is protest behaviour. If the distribution of protest responses is not independent of respondent or survey characteristics, then simply expelling protesters from surveys can lead to sample selection bias. Furthermore, WTP estimates will not be comparable across surveys. This paper seeks to explore potential causes of protest behaviour through a meta-study based on full datasets from 38 different surveys. The objective of the study is to examine the effect of respondent specific variables as well as survey specific variables on protest behaviour. Our results suggest that some of the differences in WTP typically observed between different demographic groups, different elicitation formats and different question formats might actually be attributed to inherent differences in the propensity to protest. Our results indicate that the propensity for respondents to exhibit protest behaviour when asked a stated preference type valuation question depends on a number of specific factors, respondent specific as well as survey specific—knowledge which could be used in order to reduce protest behaviour.     

A comparison of empirical models used to infer the willingness to pay in contingent valuation

The essence of the contingent valuation method consists of creating a hypothetical market where respondents are asked about their willingness to pay (WTP) for a non-market good. Different empirical models can be formulated to estimate the expected WTP of a sample of respondents and, then, through aggregation, the social valuation of the good is inferred.This paper outlines the relevance of the distributional assumptions when estimating mean WTP. Several parametric and non-parametric methods are discussed and applied to calculate the existence value of a natural space. Results show that WTP is extremely sensitive to the empirical model used.First version received: November 2002 / Final version received: January 2004     

Distal order effects in stated preference surveys

Stated preference researchers have previously demonstrated that a good's placement among a sequence of goods in a set of valuation questions (i.e. proximal order effects) can have a substantial impact on people's valuations of these different goods. However, the economic consequences of potential order effects stemming from other questions in a survey, prior to the valuation tasks, have received surprisingly little attention. Using an online climate change survey, we identify order effects created by prior attitude-elicitation questions, and we assess the potential impact of these distal order effects on willingness to pay (WTP) estimates for stylized climate change policies. We find that the order used in prior questions may change people's opinions toward various attributes of the good to be valued, and thereby change WTP by a substantial amount. This paper emphasizes the significance of order effects stemming from preliminary survey questions, and supports a call for diligence in the random ordering of all potentially influential preliminary information in stated preference surveys to minimize inadvertent effects from any single arbitrary ordering.     

The impact of the bird flu on public willingness to pay for the protection of migratory birds

In this paper, we present the results of a unique time series analysis of contingent values and models for migratory bird protection based on an identical contingent valuation (CV) survey carried out over a three year time period since the first bird flu outbreak in 2003. Although there exists no scientific evidence for a direct relationship, migratory birds are believed to play an important role in spreading the bird flu virus worldwide. The time series analysis allows us to test the temporal stability of stated preferences for migratory bird protection and at the same time examine indirectly the possible impact of increased media attention and public awareness levels regarding the bird flu. We test the impact of the bird flu on public willingness to pay (WTP) for migratory bird protection in the final 2005 survey whilst accounting for procedural variance introduced by sequencing and question ordering-effects, but we are unable to demonstrate a direct negative relationship. A novelty of the study presented here is that respondents in the CV surveys are given the opportunity to pay an annual money amount or a one-time-off lump-sum. Annual WTP values appear to be significantly higher than one-time-off WTP values, suggesting a negative implicit discount rate. Self-selection bias is an important reason for the observed differences. We find that respondents who agree to pay annually differ significantly from respondents who wish to pay a lump-sum in terms of their underlying preferences and motivations towards migratory bird protection.     

Contingent valuation: A new perspective

After several decades of academic research on the contingent valuation (CV) method a consistent behavioral explanation of ‘hypothetical bias’ is still lacking. Based on evidence from economics, economic psychology and the political sciences, I propose an explanation that is based on two simple working hypotheses about respondent behavior in contingent valuation surveys. The first hypothesis is that survey respondents are unable to form consistent preferences about unfamiliar goods unless the choice context offers reliable, informative cues which can be rationally exploited in simplified heuristics. The second hypothesis is that the probability and impact of strategic responses in dichotomous-choice questions about public goods depends on the extent to which the presented hypothetical costs differ from the actual costs. The literature on hypothetical bias is revisited in the light of these behavioral hypotheses. I find that the hypotheses are generally supported by the empirical data. Moreover, the hypotheses are able to explain several important empirical phenomena that previous research has not been able to explain. In particular, they solve the puzzle that pre-election polls, but not CV surveys, are able to predict actual referendum outcomes, and they explain why income effects on willingness to pay are lower in CV responses than in actual votes. If confirmed by further studies, the hypotheses will have important implications for future research and practice. First, the hypothetical costs presented in the dichotomous-choice question should to be close enough to the actual costs to be credible to all respondents. This can be achieved by specifying the costs as a percentage (rather than absolute) change in taxes. Second, the respondents should be given the option to answer based on information about the positions of large parties and interest groups with known political orientation rather than based on the raw policy information. Theory and evidence suggest that this new survey paradigm largely eliminates the fundamental problems of the conventional stated preference methods.     

Asking for Individual or Household Willingness to Pay for Environmental Goods?

The aggregate welfare measure for a change in the provision of a public good derived from a contingent valuation (CV) survey will be higher if the same elicited mean willingness to pay (WTP) is added up over individuals rather than households. A trivial fact, however, once respondents are part of multi-person households, it becomes almost impossible to elicit an “uncontaminated” WTP measure that with some degree of confidence can be aggregated over one or the other response unit. The literature is mostly silent about which response unit to use in WTP questions, and in some CV studies it is even unclear which type has actually been applied. We test for differences between individual and household WTP in a novel, web-administered, split-sample CV survey asking WTP for preserving biodiversity in old-growth forests in Norway. Two samples are asked both types of questions, but in reverse order, followed by a question with an item battery trying to reveal why WTP may differ. We find in a test between samples that the WTP respondents state on behalf of their households is not significantly different from their individual WTP. However, within the same sample, household WTP is significantly higher than individual WTP; in particular if respondents are asked to state individual before household WTP. Our results suggest that using individual WTP as the response unit may overestimate aggregate WTP. Thus, the choice of response format needs to be explicitly and carefully addressed in CV questionnaire design and further research in order to avoid the risk of unprofitable projects passing the benefit-cost test.

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Preference Structures, Property Rights, and Paired Comparisons

The method of paired comparisons was used to determine the structure of survey participants' value expressions for Australian native forests. The same participants were also surveyed using the contingent valuation method (CVM). Data from the paired comparisons were used to construct preference maps which enabled identification of participants whose value expressions were structurally incompatible with economic welfare theory – in particular, those participants who expressed their values according to lexicographic preferences. For some of these participants, CVM results did not provide appropriate measures of WTP. The surveys also demonstrated the importance of allowing participants' own views on property rights to dictate the valuation context offered.     

Exchange Rules and the Incentive Compatibility of Choice Experiments

The incentive properties of stated-preference surveys continue to be a central debate in the valuation of public goods. The majority of empirical studies have focused on incentive properties of contingent valuation questions in relation to situations where answers have monetary consequences. This research explores the incentive properties of repeated, attribute-based choice questions when subjects are provided with an explicit connection between choices and outcomes. Two market/provision-rules are investigated: a posted-price market and a plurality-rule vote. These two provision rules are contrasted to treatments in which no provision rule is discussed—subjects are simply asked to choose their preferred alternative. These three hypothetical choice treatments are compared with a binding choice treatment. While none of the public good treatments are theoretically incentive compatible, we include a comparison of hypothetical and binding choices for a private-good that is incentive compatible. The private good experiments indicate that marginal willingness to pay (WTP) estimates from the hypothetical treatment are larger, but not statistically different than corresponding estimates in the binding choice treatment. Results for the public good experiments indicate that marginal WTP estimates from the hypothetical treatments are much larger, and statistically different than corresponding estimates in the binding choice treatment. The bias is largest when no provision rule is discussed. The bias is reduced with the inclusion of a provision rule, but surprisingly, there was no difference across provision rule treatments. Overall, our results indicate that choice experiments involving a public good should include a provision rule to reduce bias, but the resulting marginal WTP estimates may still be more biased, on average, than those arising from contingent valuation survey formats.     

Multivariate Mixed Models for Open-Ended Contingent Valuation Data: Willingness To Pay For Conservation of Monk Seals

Although dichotomous choice (DC) contingent valuation (CV) has been recommended by the US NOAA 'blue-ribbon' panel for large-scale contingent valuation studies, useful information can still be obtained from smaller, open-ended (OE) studies, often undertaken as a precursor to a DC survey. The CV study considered here was carried out in Greece and looked at willingness-to-pay (WTP) for protecting the Mediterranean monk seal (Monachus-monachus) in the Aegean area. This is the most endangered seal in the world, and the application of the CV methodology was the first such application in Greece. The OE data consist of two responses: first, a binary response detailing whether or not respondents were in principle prepared to pay for the protection of this seal; secondly, those respondents who answered 'yes' to the first question were then asked to state their maximum WTP for such protection. A multivariate binomial – log-normal mixture model is used to develop a bid function including explanatory variables such as income, sex, age and education. Such a modelling approach provides an alternative to more commonplace tobit estimation. However, the model is extended to include further information which was collected on:(a) an increased WTP amount given in response to information that the initial WTP amount may not be enough to prevent the extinction of the seal;(b) respondents were asked to divide their final WTP amount between use, option and existence values, the latter requiring a multivariate model with four binary and four continuous responses per individual in the same model.The discussion focuses on the methodological issues raised with some comment on the substantive interpretation of results.     

The effect of individual ‘ability to choose’ (scale heterogeneity) on the valuation of environmental goods

Environmental valuation methods, such as choice experiments, are increasingly being used to value complex and often unfamiliar environmental goods. A potential risk is that some survey respondents may not be capable of developing and expressing preferences for such goods. The noise from these individuals may then conceal the well-defined preferences of other respondents and affect valuation estimates. We address this problem by estimating a range of models that accounts for scale heterogeneity (which we interpret as a respondent's ability to choose: ATC) and taste heterogeneity. These models are applied to two case studies: amenity from coastal defence and biodiversity. In both case studies, model fit was improved in a scale-heterogeneity multinomial-logit (S-MNL) model (compared to a standard MNL model) suggesting the accounting for ATC (scale heterogeneity) improved preference revelation. A mixed multinomial-logit (MIXL) model outperformed the S-MNL model suggesting that accounting for taste heterogeneity was also important. However, a generalised multinomial-logit (G-MNL) model improved model fit over the MIXL model only for the biodiversity data suggesting that for these data both taste heterogeneity and ATC were important. We conclude that accounting for ATC can improve the reliability and robustness of the results when valuing complex or unfamiliar environmental goods.     

Respondent direct experience and contingent willingness to pay for new commodities: a switching endogenous interval regression analysis

Most environmental economists argue that direct experience with the good being valuated, or with similar goods, is a precondition for providing valid willingness to pay (WTP) responses to contingent valuation questions. Two questions are posed in this article. The first is whether previous use experience of a resource (Séné nature reserve) similar to that being valuated (future nature reserves) and located in the same geographical area (Gulf of Morbihan) impacts on WTP. The second is whether accounting for the endogeneity of direct experience matters in the estimation of WTP. We find that respondents who have not experienced the Séné nature reserve provide value estimates that are statistically comparable to that of respondents who have experienced it. Our assumption is that respondents have acquired sufficient and adequate experience of future nature reserves from the questionnaire that experience obtained by experiencing the Séné nature reserve was not necessary for making a valid value formulation. Hence, aggregation of WTP estimates to obtain a total valuation of the future nature reserves is reasonable over the full target population. In addition, our results show that direct experience is endogenously determined; but controlling for the endogeneity has a marginal effect on WTP estimates.     

External Tests of Scope and Embedding in Stated Preference Choice Experiments: An Application to Endangered Species Valuation

A criticism often levied against stated preference (SP) valuation results is that they sometimes do not display sensitivity to differences in the magnitude or scope of the good being valued. In this study, we test the sensitivity of preferences for several proposed expanded protection programs that would protect up to three US Endangered Species Act-listed species: the Puget Sound Chinook salmon, the smalltooth sawfish, and the Hawaiian monk seal. An external scope test is employed via a split-sample SP choice experiment survey to evaluate whether there is a significant difference in willingness to pay (WTP) for protecting more species and/or achieving greater improvements in the status of the species. The majority of 46 scope tests indicate sensitivity to scope, and the pattern of scope test failures is consistent with diminishing marginal utility with respect to the amount of protection to each species. Further tests suggest WTP may be proportional to the number of species valued.     

Depletion,climate, and the incremental value of groundwater

Groundwater provides vital inputs to crop production and contributes to rural economies throughout the world. Research on the economic benefits associated with groundwater resources has typically focused on the impacts of groundwater availability on the profitability of agricultural production or on the non-market benefits associated with groundwater quality for human consumption. In this research, we use stated-preference methods to investigate the total economic value to agricultural producers of an increase in groundwater availability in the Ogallala Aquifer region. The contingent valuation method allows for estimation of values beyond agricultural profitability, including non-market values such as the ability to leave additional groundwater to future generations. We find a median willingness to pay (WTP) for an additional 100 gallons per minute of well capacity of $77 per well, and that this estimate depends strongly on current well capacity and climate conditions. For counties in hotter and drier regions of the aquifer with low well capacity, median WTP is significantly higher. These results are then used in conjunction with projections of future climate and groundwater availability to generate predicted changes in the WTP for additional groundwater across the aquifer. This research provides important feedback on how the benefits of additional groundwater availability are predicted to change as groundwater resources are diminished in a changing climate.     

Proportionality of Willingness to Pay to Small Changes in Risk: The Impact of Attitudinal Factors in Scope Tests

Sensitivity (proportionality) of willingness to pay (WTP) to (small) risk changes is often used as a criterion to test for valid measures of economic preferences. In a contingent valuation (CV) study conducted in Austria, 1,005 respondents were asked their WTP for preventing an increase in the risk of being killed in an avalanche of 1/42,500 and 3/42,500 respectively. WTP for the higher variation in risk is significantly greater than WTP for the lower risk change. We find evidence that those respondents who have had personal experience of avalanches in recent years combine the information about future risk increase—as provided in the survey—with the observed number of fatal avalanche accidents in the past. Proportionality of WTP holds if such prior experience is taken into account and if attitudinal factors in scope tests are controlled for. This research was funded by alpS GmbH—Center for Natural Hazard Management, Innsbruck, Austria.