Browsing by Author "de Dios Ortuzar, Juan"
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- ItemCan mixed logit reveal the actual data generating process? Some implications for environmental assessment(PERGAMON-ELSEVIER SCIENCE LTD, 2010) Cherchi, Elisabetta; de Dios Ortuzar, JuanRecent advances in the specification of the utility function of mixed logit models allow the analyst, in principle, to consider a vast variety of individual heterogeneity. Nevertheless, when estimating the model it is common practice to experience severe difficulties in discriminating between different specifications to infer the "true" data generating process. We investigate possible sources for this difficulty focusing on the confounding effects inherent in two basic assumptions of discrete choice model utilities: linearity in the parameters and added error terms. We analyse the role of these assumptions in giving rise to confounding effects and why this increases the difficulty of discriminating among different structures. Finally, we investigate how these problems may affect benefit appraisal using these models. Empirical evidence is provided for two different environmental contexts and a more typical transport context using various kinds of data. (C) 2010 Elsevier Ltd. All rights reserved.
- ItemCosting school transport in Spain(TAYLOR & FRANCIS LTD, 2006) Ibeas, Angel; Luis Moura, Jose; Dell'olio, Luigi; de Dios Ortuzar, JuanSchool transport in Spain is conceived administratively as a regular, but special, public transport service financed by the Spanish regional governments through private sector contracts adjudicated by public tendering. As such it has two special features in comparison to systems elsewhere. First, larger operators use conventional buses (rather than special school buses) and these can also be used for regular services during school hours. Second, as these are regional services, often only regional operators bid for these tenders, so contract assignment resembles a bargaining process between operators and administrations, tempering an adequate operation of the market. This problem is common to all Spanish regions. The situation described has generated high costs (i.e. 15% increase in contract costs in the past year although the number of contracts did not vary significantly). For this reason the Government of Cantabria commissioned research to examine the problem. A simple cost allocation model allowed us to detect that school transport costs were, on average, approximately 18% higher than what could be deemed reasonable. This article describes the problem, the reasons why it has occurred and explains the model built to examine it in certain detail. It also shows the immediate consequences of its application (i.e. the reaction of the main operators and their changed strategy) and the steps taken by the Regional Government, based on our results, to ensure a proper operation of the market in the future.
- ItemDefining Interalternative Error Structures for Joint Revealed Preference-Stated Preference Modeling New Evidence(SAGE PUBLICATIONS INC, 2010) Francisca Yanez, Maria; Cherchi, Elisabetta; de Dios Ortuzar, JuanJoint model estimation with revealed (RP) and stated preference (SP) data has become popular in the past few years, and it is now considered common practice. Many theoretical issues related to estimation and prediction with joint RP-SP data are far from being fully explored. Given the ample diffusion of RP-SP modeling in practice, its misuse can have severe consequences on policy analysis and evaluation of transport investments; thus, it is crucial to continue research on this problem to try to give a theoretical justification to the many relevant issues that remain uncovered. One particularly interesting issue, which has not been well explored, is the effect of partial data enrichment on the correlation structure of alternatives (i.e., when different correlation structures are revealed in the RP and SP data sets). This problem, which is often found in practice, has no trivial solution and raises new interesting theoretical questions about estimation and prediction. In this paper, theoretical and practical implications of this problem are discussed and then empirical evidence is provided, from a real case, of the errors that may creep in when these models are not applied correctly. Finally some guidelines to help fill this important gap in the proper use of RP-SP data are provided.
- ItemEstimating the Value of Risk Reduction for Pedestrians in the Road Environment: An Exploratory Analysis(ELSEVIER SCI LTD, 2011) Hensher, David A.; Rose, John M.; de Dios Ortuzar, Juan; Rizzi, Luis I.In recent years there has been a re-focus on the valuation of a statistical life from the ex post or human capital method to an ex ante willingness to pay (WTP) approach. This is in part a recognition that we need to focus on establishing the amount, ex ante, that individuals are willing to pay to reduce the risk of exposure to circumstances that might lead to death or degree of injury in the road environment. This study sets out a framework in which to identify the degree of preference heterogeneity in WTP of pedestrians to avoid being killed or injured. A stated choice experiment approach is developed. The empirical setting is a choice of walking route for a particular trip that a sample of pedestrians periodically undertakes in Australia. Mixed logit models are estimated to obtain the marginal (dis)utilities associated with each influence on the choice amongst the attribute packages offered in the stated choice scenarios. These conditional estimates are used to obtain the WTP distributions for fatality and classes of injury avoidance, which are then aggregated to obtain estimates for pedestrians of the value of risk reduction (VRR).
- ItemEstimating the willingness to pay and value of risk reduction for car occupants in the road environment(PERGAMON-ELSEVIER SCIENCE LTD, 2009) Hensher, David A.; Rose, John M.; de Dios Ortuzar, Juan; Rizzi, Luis I.In recent years there has been a re-focus on the valuation of a statistical life from the ex post or human capital method to an ex ante willingness to pay (WTP) approach. This is in part a recognition that we may have been undervaluing the cost of fatalities and injuries to society associated with crashes, but also a strong belief in the need to focus on establishing the amount, ex ante, that individuals are willing to pay to reduce the risk of exposure to circumstances that might lead to death or degree of injury on the road network. This study has developed a framework in which to identify the degree of preference heterogeneity in willingness to pay by individuals who are drivers or passengers in cars to avoid being killed or injured. A stated choice experiment approach is developed. The empirical setting is a choice of route for a particular trip that a sample of individuals periodically undertakes in Australia. The particular trip is described in enough detail to provide the respondent with a familiar market environment, providing all the relevant background information required for making a decision. Mixed logit models are estimated to obtain the marginal (dis)utilities associated with each influence on the choice amongst the attribute packages offered in the stated choice scenarios. These estimates are used to obtain the WTP distributions for fatality and injury avoidance, which are then aggregated to obtain estimates of the value of risk reduction (VRR), of which the fatality class is also known as the value of a statistical life (VSL). (C) 2009 Elsevier Ltd. All rights reserved.
- ItemOn the Use of Mixed RP/SP Models in Prediction: Accounting for Systematic and Random Taste Heterogeneity(INFORMS, 2011) Cherchi, Elisabetta; de Dios Ortuzar, JuanA basic assumption in mixed revealed preference (RP)/stated preference (SP) estimation is that both data sets represent basically the same phenomenon. Thus, we would expect individuals to show the same tastes regardless of the tool used to elicit their preferences. However, different and significant parameters are often found in each case. Although this is not an issue from an estimation standpoint, understanding why differences appear is crucial in forecasting because the model structure used in that case differs from the estimated one. This problem is compounded if differences between both data affect their ability to reproduce systematic or random taste variations because (i) microeconomic conditions on individual behaviour are more difficult to fulfil, and (ii) an erroneous specification may have a major impact on the predicted results. Problems associated with using joint RP/SP models in forecasting have received scant attention and no studies have examined the case where both types of data show different systematic or random heterogeneity. We review the problem from a theoretical viewpoint and suggest analyses that could aid decision taking in this context. Using real data, we provide evidence on the effects of using different joint RP/SP models in forecasting and highlight the importance of performing these analyses.
- ItemSea urchin: From plague to market opportunity(ELSEVIER SCI LTD, 2012) Grisolia, Jose M.; Lopez, Francisco; de Dios Ortuzar, JuanThe coast line of the Canary Islands (Spain) has suffered from a plague of Diadema antillarum (sea urchin) over the last decades. This has attracted the attention of local authorities since it is becoming a serious environmental problem. We set out to analyse the potential market for sea urchin meat in this region, where this species is not subject to commercial exploitation and it is relatively unknown. The paper uses data from a sample of volunteers who were interviewed before and after tasting different dishes cooked with sea urchin. We applied discrete choice models considering that answers before and after experiencing this food belonged to different types of data: this is a mixed data approach in the state of practice. Our main conclusion is that there is indeed a market niche for having specialised restaurants serving sea urchin as a delicacy food. (C) 2012 Elsevier Ltd. All rights reserved.
- ItemThe Stochastic Satisficing model: A bounded rationality discrete choice model(2018) Gonzalez-Valdes, Felipe; de Dios Ortuzar, Juan; CEDEUS (Chile)