A Meta-analysis of Hypothetical Bias in Stated Preference Valuation

Individuals are widely believed to overstate their economic valuation of a good by a factor of two or three. This paper reports the results of a meta-analysis of hypothetical bias in 28 stated preference valuation studies that report monetary willingness-to-pay and used the same mechanism for eliciting both hypothetical and actual values. The papers generated 83 observations with a median ratio of hypothetical to actual value of only 1.35, and the distribution has severe positive skewness. We find that a choice-based elicitation mechanism is important in reducing bias. We provide some evidence that the use of student subjects may be a source of bias, but since this variable is highly correlated with group experimental settings, firm conclusions cannot be drawn. There is some weak evidence that bias increases when public goods are being valued, and that some calibration methods may be effective at reducing bias. However, results are quite sensitive to model specification, which will remain a problem until a comprehensive theory of hypothetical bias is developed.JEL classifications: C9, H41, Q26, Q28     

Aggregation Biases in Stated Preference Studies

Stated preference studies are often used to provide estimates of non-market values for cost-benefit analysis. Applications of these techniques have been criticised because of the hypothetical nature of the surveys and the possibility of bias. Various types of bias have been cited including strategic, payment vehicle, starting point, interviewer and others. However, one type of bias that has received limited attention, but has the potential to have substantial impacts on value estimates, is that associated with aggregation. In this paper the theoretical basis for aggregation is explored, and alternative approaches for aggregation are trialed. It is demonstrated that the choices made by researchers at this stage of the value estimation process can significantly affect the estimates that are to be used in cost-benefit analyses.     

A Common Nomenclature for Stated Preference Elicitation Approaches

It is often difficult to determine what actually was done in work involving data collected with stated preference surveys because the terms used to describe various procedures have ambiguous and sometimes conflicting meanings. Further, terms used to describe data collection procedures often are confounded with terms used to describe statistical techniques. We call for the use of a common nomenclature to describe what was done in a data collection effort for stated preference studies, and take a first step at setting out such nomenclature. We only seek to improve clarity in the communication of research results and take no position here on appropriateness of particular procedures.     

Combining Revealed Preference Data with Stated Preference Data: A Latent Class Approach

A substantial literature exists combining data from revealed preference (RP) and stated preference (SP) sources, aimed either at testing for the convergent validity of the two approaches used in nonmarket valuation or as a means of drawing on their relative strengths to improve the ultimate estimates of value. In doing so, it is assumed that convergence of the two elicitation approaches is an “all or nothing” proposition; i.e., the RP and SP data are either consistent with each other or they are not. The purpose of this paper is to propose an alternative framework that allows for possible divergence among individuals in terms the consistency between their RP and SP responses. In particular, we suggest the use of a latent class approach to segment the population into two groups. The first group has RP and SP responses that are internally consistent, while the remaining group exhibits some form of inconsistent preferences. An EM algorithm is employed in an empirical application that draws on the Alberta and Saskatchewan moose hunting data sets used in earlier combined RP and SP exercises. The empirical results suggest that somewhere between one-third and one-half the sample exhibits consistent preferences. We also examine differences in welfare estimates drawn from the two classes.     

Appropriate Payment Vehicles in Stated Preference Studies in Developing Economies

Selecting appropriate payment vehicles is critical for the perceived consequentiality and incentive compatibility of stated preferences surveys. We analyze the performance of three different payment vehicles in a Malaysian case of valuing wetland conservation. Two are well-known: voluntary donations and income taxes. The third is new: reductions in government subsidies for daily consumer goods. Using donations is common, but this payment vehicle is prone to issues of free-riding. An income tax usually has favorable properties and is commonly used in environmental valuation. However, in Malaysia as well as in many other low- to middle-income economies, large proportions of people do not pay income taxes, putting the validity of this payment vehicle into question. Instead, citizens in Malaysia and many other countries benefit from subsidies for a range of consumer goods. We find that price sensitivity is higher and the unexplained variance smaller when using subsidies rather than donations or income taxes. Importantly, this approach translates into completely different conclusions concerning policy advice. Our results suggest that in developing countries, using reduced subsidies as a payment vehicle may have favorable properties in terms of improved payment consequentiality compared to alternative payment vehicles, thus enhancing the external validity of stated preference surveys.     

Understanding Hurricane Evacuation Decisions Under Contingent Scenarios: A Stated Preference Approach

We conduct a stated preference analysis to understand the factors that individual households take into consideration to evacuate during hurricanes. In designing the contingent scenarios for evacuation, we randomly assign varying levels of hurricane characteristics (wind speed, lead time for landfall and the height of storm surge) combined with different types of emergency management options (voluntary versus mandatory evacuation order and a voucher with varying amounts to cover evacuation expenses). Findings indicate that individual households respond, in a non-linear fashion, to the intensity of hurricanes when making evacuation decisions. Respondents are also more likely to evacuate when the storm surge reaches a certain threshold. In terms of policy interventions, mandatory evacuation orders are more effective to increase the likelihood of evacuation. The potential intervention in the form of providing evacuation vouchers to assist households to cover their expenses (e.g. for food, water, transportation and lodging) also seems effective. We discuss policy implications of our findings.     

Using Labels to Investigate Scope Effects in Stated Preference Methods

Insufficient sensitivity to scope (variations in the scale of the environmental good on offer) remains a major criticism of stated preference methods, and many studies fail a scope test of some sort. Across a range of existing explanations for insensitivity to scope (commodity mis-specification, embedding, warm glows) there seems to exist no clear conclusion on how to deal with the problem. This paper provides an alternative explanation for insufficient sensitivity to scope, based on re-definition of the determinants of value for environmental goods within an attributes-based choice model. In the proposed framework respondents’ Willingness To Pay need depend not only on physical characteristics of a good, but may also depend on the ‘label’ under which the environmental good is ‘sold’ in the hypothetical market. To investigate this problem, a Choice Experiment study of biodiversity was conducted. We find that controlling for the effects of a label—in this case, national park designation—leads to significant increase in the scope sensitivity of welfare measures.     

Anomalies and Stated Preference Techniques: A Framework for a Discussion of Coping Strategies

This paper introduces a symposium on the issue of how stated preference (SP) research can best cope with ‘anomalies’ (i.e. systematic deviations from the predictions of standard economic theory) in survey responses. It proposes a framework for constructive debate, recognising (i) the legitimate aspirations of SP research, (ii) the relevance of evidence from sources other than best-practice SP, and (iii) the precautionary value of investigating strategies for coping with suspected anomalies, even if questions about the robustness of anomalies have not been finally resolved. Five alternative coping strategies, discussed in more detail in the symposium, are briefly introduced. JEL classifications: D61, D63, Q51     

Modeling Spatial Patchiness and Hot Spots in Stated Preference Willingness to Pay

Stated preference analyses often impose strong assumptions regarding spatial welfare distributions that can influence the validity of welfare analysis and aggregation. These include spatial homogeneity and continuous distance decay. Global assumptions such as these are increasingly questioned by non-economics disciplines in favor of approaches that allow for local patchiness. Drawing from this literature, this article proposes methods to identify and evaluate hot spots in stated preference welfare estimates using local indicators of spatial association. Methods are illustrated using geocoded choice experiment data addressing river restoration. Results suggest the presence of statistically significant, non-continuous patterns overlooked by current approaches.     

Sex Preference, Marriage of Heirs and Bequest Behaviour

This paper discusses some economic implications of sex preferences and the bequest behaviour of parents. A simple two-period model with general assumptions is developed. It is shown that a Nash equilibrium does not exist unless constraints are imposed. However, such an equilibrium exists if bequests are non-negative, if bequests to sons and daughters are equal or if preferences are heterogeneous. The model thus explains why such institutional constraints on bequests are observed in the real world, and why in some (developing) countries male children inherit the major wealth from parents. It also has useful implications for the debt neutrality proposition.
JEL Classification Numbers: D1, J12, J13, J16.     

Context and the VSL: Evidence from a Stated Preference Study in Italy and the Czech Republic

We report on the results of a survey based on conjoint choice experiments that was specifically designed to investigate the effect of context on the Value of a Statistical Life (VSL), an important input into the calculation of the mortality benefits of environmental policies that reduce premature mortality. We define “context” broadly to include (1) the cause of death (respiratory illness, cancer, road traffic accident), (2) the beneficiary of the risk reduction (adult v. child), and (3) the mode of provision of the risk reduction (public program v. private good). The survey was conducted following similar protocols in Italy and the Czech Republic. When do not distinguish for the cause of death, child and adult VSL are not significantly different from one another in Italy, and the difference is weak in the Czech sample. When we distinguish for the cause of death, we find that child and adult VSLs are different at the 1% level for respiratory illnesses and road-traffic accidents, but do not differ for cancer risks. We find evidence of a “cancer premium” and a “public program premium.” In both countries, the marginal utility of income is about 20% lower among wealthier people, which makes the VSL about 20% higher among respondents with incomes above the sample average. The discount rate implicit in people’s choices is effectively zero. We conclude that there is heterogeneity in the VSL, and that such heterogeneity is primarily driven by risk characteristics mode of delivery of the risk reduction, and income, while other individual characteristics of the respondent (e.g., age and education) are less important. For the most part, our results are in agreement with environmental policy analyses that use the same VSL for children and adults, and that apply a cancer premium.     

Valuing Changes in the Quality of Coral Reef Ecosystems: A Stated Preference Study of SCUBA Diving in the Bonaire National Marine Park

We estimated the economic value of changes in the quality of a coral reef ecosystem to SCUBA divers in the Caribbean using a stated preference mail survey. Our sampling frame was all divers with U.S. home addresses who purchased a tag required for diving in the Bonaire National Marine Park in 2001. Divers were asked how they might have altered their trip choice had the quality of the coral reef system been different from what they experienced. From these responses we inferred the value of three different levels of quality defined by visibility, species diversity, and percent coral cover. We used random utility theory and mixed logit to analyze the choice questions. Our sample size was 211, and our survey response rate was 75%. For modest changes in quality we estimated per person annual losses at $45. For larger losses the value was $192. Presented at the 3rd World Congress of Environmental and Resource Economists in Kyoto, Japan, July 2006.     

Contribution of Contingent Valuation and Other Stated Preference Methods to Evaluation of Environmental Policy

Some form of stated preference method is essential for comprehensive evaluation of environmental policy options. The two most important stated preference methods are contingent valuation (CV) and choice modelling. I identify and discuss the major challenges facing CV and choice modelling researchers. Choice modelling applications to environmental valuation are comparatively recent, so the emphasis in this paper is on the more extensive body of CV research. The development of CV has been characterised by a (generally) constructive debate both within the economics profession, and between economists, philosophers, psychologists and other social scientists. As a result, much has been learnt about the nature of non-market economic values and how they might be measured. Important issues are the extent to which existing stated preference methods accurately represent individuals' values, and provide valid and reliable measures of changes in economic welfare. I review each of these issues in the light of recent theoretical and empirical work, identify the major outstanding problems, and indicate areas where progress is being made. I argue that the problems are solvable, and that eventually a theoretically sound and empirically effective method will be developed.     

As Time Goes By: Examination of Temporal Stability Across Stated Preference Question Formats

We evaluate the temporal stability of willingness-to-pay values obtained from two identical stated-preference surveys undertaken in 2004 and 2012. The surveys employ two discrete-choice elicitation formats to value reductions in two health endpoints related to tap water consumption, and are explicitly designed to make direct comparisons between formats. We find no significant differences in real willingness-to-pay between the two surveys for either format—a result that is robust to the structure of heterogeneity used to model respondent preferences. Findings lend support, at least within the context of tap water quality, to the temporal transfer of nonmarket benefits over extended time periods.     

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.     

Identifying Water Prices at which Australian Farmers Will Exit Irrigation: Results of a Stated Preference Survey

Among the measures taken by the Australian government to address one of the worst droughts on record in the Murray‐Darling Basin, exit package issues have rarely been investigated. A stated preference survey was designed to identify the range of water prices required for irrigators to sell all their water entitlements and leave the irrigation industry. Farmer participation responses are generally price elastic. There are large regional differences in price elasticities, but within a region there are few differences based on subgroups of farmers.     

A Split-Sample Revealed and Stated Preference Demand Model to Examine Homogenous Subgroup Consumer Behavior Responses to Information and Food Safety Technology Treatments

The combination and joint estimation of revealed and stated preference (RP/SP) data approach to examining consumer preferences to relevant policy-based measures typically fail to account for heterogeneity in the data by considering behavior of the average individual. However, in policy-based analyses, where the research is often driven by understanding how different individuals react to different or similar scenarios, a preferred approach would be to analyze preferences of homogenous population subgroups. We accomplish this by developing a split-sample RP/SP analysis that examines whether homogenous subgroups of the population, based on individual health and behavioral characteristics, respond differently to health-risk information and new food safety technology. The ongoing efforts by the US Food and Drug Administration (FDA) to reduce illness and death associated with consuming raw Gulf of Mexico oysters provide an ideal platform for the analysis as the health risks only relate to a very specific consumer subgroup. Results from split-sample demand models indicate that educational information treatments cause vulnerable at-risk consumers to reduce their oyster demand, implying that a more structured approach to disseminating the brochures to the at-risk population could have the desired result of reducing annual illness levels. Also, findings across all subgroups provide strong empirical evidence that the new FDA policy requiring processing technology to be used in oyster production will have a detrimental effect on the oyster industry.