A Bayesian perspective on sampling of alternatives

In this paper, we apply a Bayesian perspective to the sampling of alternatives for multinomial logit (MNL) and mixed multinomial logit (MMNL) models. A sampling of alternatives reduces the computational challenge of evaluating the denominator of the logit choice probability for large choice sets by only using a smaller subset of sampled alternatives including the chosen alternative. To correct for the resulting overestimation of the choice probability, a correction factor has to be applied. McFadden (1978) proposes a correction factor to the utility of each alternative which is based on the probability of sampling the smaller subset of alternatives and that alternative being chosen. McFadden's correction factor ensures consistency of parameter estimates under a wide range of sampling protocols. A special sampling protocol discussed by McFadden is uniform conditioning, which assigns the same sampling probability and therefore the same correction factor to each alternative in the sampled choice set. Since a constant is added to each alternative the correction factor cancels out, but consistent estimates are still obtained. Bayesian estimation is focused on describing the full posterior distributions of the parameters of interest instead of the consistency of their point estimates. We theoretically show that uniform conditioning is sufficient to minimise the loss of information from a sampling of alternatives on the parameters of interest over the full posterior distribution in Bayesian MNL models. Minimum loss of information is, however, not guaranteed for other sampling protocols. This result extends to Bayesian MMNL models estimated using the principle of data augmentation. The application of uniform conditioning, a more restrictive sampling protocol, is thus sufficient in a Bayesian estimation context to achieve finite sample properties of MNL and MMNL parameter estimates

Sharing the Burden of Adaptation Financing: An Assessment of the Contributions of Countries

Climate change may cause most harm to countries that contribute least to greenhouse gas emissions. This paper identifies deontology, solidarity and consequentialism as the principles that can serve as a basis for a fair international burden sharing scheme of adaptation costs. We translate these principles into criteria that can be applied in assigning contributions of individual countries, namely historical responsibility, equality and capacity to pay. Specific political and scientific choices are discussed, highlighting implications for international burden-sharing. Combining historical responsibility and capacity to pay seems a promising starting point for international negotiations on the design of burden-sharing schemes. From the numerical assessment, it is clear that UNFCCC Annex I countries carry the greatest burden under most scenarios, but contributions differ substantially subject to the choice of an indicator for capacity to pay. The total financial contribution by the Annex I countries could be in the range of $55-68 billion annually.Adaptation Financing, Burden-Sharing, Historical Responsibility

Inciting protocols

This paper studies patenting decisions by firms in relation to the negotiation and signing of the Helsinki and Oslo protocol as part of the Convention on Long-Range Transboundary Air Pollution. We use a uniquely constructed patent data set on SO 2 abatement technologies filed in 15 signatory and non-signatory countries in the period 1970-1997. The data distinguish between so-called 'mother' patents, or original inventions, and 'family' patents, which represent the same invention but are patents filed in foreign countries. Our analysis suggests that not only local environmental regulations matter for patenting decisions. International environmental agreements provide incentives for additional inventive activity in and the diffusion of knowledge towards signatory countries by reducing investment uncertainty for inventing firms

Daily physical activity patterns in cancer survivors: a pilot study

In cancer survivors activity levels have been studied primarily by means of questionnaires, while objective information on actual daily activity levels and their distribution throughout the day is lacking. The findings of this study suggest that especially cancer survivors who received chemotherapy as part of their treatment, have low physical activity levels. However, this study did not found support for a deviating daily activity pattern in cancer survivors compared to healthy controls. Since information on daily activity patterns is important for the development of new interventions to improve post cancer activity behavior, additional research is needed to determine if a larger study sample supports the findings of this pilot study

Impact of travel time constraints on taste heterogeneity and non-linearity in simple time-cost trade-offs

Discrete choice models are a key technique for estimating the value of travel time (VTT). Often, stated choice data are used in which respondents are presented with trade-offs between travel time and travel cost and possibly additional attributes. There is a clear possibility that some respondents experience time constraints, leaving some of the presented options unfeasible. A model not incorporating information on these constraints would explain choices for faster and more expensive options as an indication that those respondents have a higher VTT when in reality they may be forced to select the more expensive option as a result of their personal constraints. This paper puts forward the hypothesis that this can have major impacts on findings in terms of heterogeneity in VTT measures. This paper examines via simulation the bias in VTT estimates and especially preference heterogeneity when such constraints are (not) accounted for. Empirical evidence is provided that preference heterogeneity is confounded with the travel budget impact on the availabilities of alternatives, and it is shown that there is a risk of producing biased estimates for appraisal VTT if studies do not explicitly model choice set formation. The inclusion of an opt-out alternative could be an effective measure to reduce the bias. This paper also explores the potential use of non-linear functional forms to capture the time budget impacts

The Role of Patients' Age on Their Preferences for Choosing Additional Blood Pressure-Lowering Drugs:A Discrete Choice Experiment in Patients with Diabetes

ObjectivesTo assess whether patients' willingness to add a blood pressure-lowering drug and the importance they attach to specific treatment characteristics differ among age groups in patients with type 2 diabetes.Materials and MethodsPatients being prescribed at least an oral glucose-lowering and a blood pressure-lowering drug completed a questionnaire including a discrete choice experiment. This experiment contained choice sets with hypothetical blood pressure-lowering drugs and a no additional drug alternative, which differed in their characteristics (i.e. effects and intake moments). Differences in willingness to add a drug were compared between patients = 75 years (aged) using Pearson chi(2)-tests. Multinomial logit models were used to assess and compare the importance attached to the characteristics.ResultsOf the 161 patients who completed the questionnaire, 151 (72%) could be included in the analyses (mean age 68 years; 42% female). Aged patients were less willing to add a drug than non-aged patients (67% versus 84% respectively; P = 0.017). In both age groups, the effect on blood pressure was most important for choosing a drug, followed by the risk of adverse drug events and the risk of death. The effect on limitations due to stroke was only significant in the non-aged group. The effect on blood pressure was slightly more important in the non-aged than the aged group (P = 0.043).ConclusionsAged patients appear less willing to add a preventive drug than non-aged patients. The importance attached to various treatment characteristics does not seem to differ much among age groups.</p

Incorporating needs-satisfaction in a discrete choice model of leisure activities

In this paper we extend the behavioural scope of discrete choice models for leisure activity-travel choices. More specifically, we investigate to what extent choices for leisure activities and related travels are driven by the satisfaction of needs. In addition to conventional attributes (such as activity costs), our regret based discrete choice model incorporates latent variables representing the anticipated level of individual needs-satisfaction by a particular leisure activity. The latent variables are calibrated with the help of subjective indicators of needs-satisfaction associated with the leisure activities. Results show that needs-satisfaction allows us to decompose a substantial share of the unobserved heterogeneity in leisure activity-travel decisions across respondents. Identifying the structural drivers of anticipated needs-satisfaction also enables a better prediction of leisure activity choice

Validity and Reliability

AbstractThis chapter concerns different aspects of validity and reliability of a discrete choice experiment. Firstly, it focuses on three essential concepts for assessing the validity of the welfare estimates obtained in the choice experiment, namely content, construct and criterion validity. Secondly, it discusses how the reliability of the recorded choices can be assessed. It then discusses issues related to model comparison and selection. Finally, it addresses prediction in discrete choice models as a way to assess the quality of a model