2,124 research outputs found
Independence, homoskedasticity and existence in random utility models
Introduction
Random utility models are often characterised by descriptions such as âhomoskedasticâ or âindependentâ in the utilities of the alternatives. However these descriptions do not have meaning in any absolute sense and must therefore be used with care. It is the main aim of this paper to demonstrate this point and discuss the issues it raises. In particular, the discussion leads into a consideration of the circumstances under which the models can be said to exist.
The paper gives a definition of random utility models and goes on the define a large sub-class of those models, the additive stimulus models, on which the main discussion of the paper is focussed. The area of discussion is further specified by relating the probability statement, which is the main form in which the model is estimated and used, to the utility and utility difference distributions. New concepts are introduced of indistinguishability and almost-indistinguishability, which can be used in assessing discrete choice models. The paper then shows how a reasonable notion of model structure can be interpreted in terms of utility difference distributions for a class of indistinguishable models.
The discussion of the independence of the utility distributions of the alternatives is based on the concepts introduced in the early parts of the paper. This discussion shows that many indistinguishable models exist for which the correlation of the utility functions is radically different. A following discussion goes on to show that the notion of heteroskedasticity is similarly incapable of clear definition, even within classes of indistinguishable models.
The final main section discusses the issue of existence, finding that it is quite difficult to ensure that models actually represent a ârealâ situation, although it is seen as important that the models actually âexistâ in some sense.. An error components approach, whether using purely probit models or substituting a logit kernel appears a useful approach to maintaining the ârealityâ of the model
Discovery Through The Art Of Making
Between growing up on a farm, and working in a saddle shop, I have been conditioned to understand my environment in an empirical and experiential manner. There is a certain kind of education that can only be achieved through working with your hands, and the knowledge obtained in that fashion cannot be sufficiently translated through the written word, or with the use of technology. It is important to me to keep this type of education alive. I have disciplined myself to learning the traditional printmaking techniques of engraving and lithography for their laborious hands on qualities so that I can better understand how labor with material provokes a unique understanding of the world. Through observation, I address the slightest texture and description of a surface; I search for a relationship that may spark an epiphany, or an intuitive perception of that object or insight into reality. The mark-making systems that I develop through my continued education of the processes of engraving and lithography brings forth an authorship that is unique to me and only my hand can create. Utilizing flat files, card catalogs, and wall placement as formats for presenting works; I am conveying a didactic quality that provokes an intimate sensation of discovery. I bring the viewer an understanding of how through meticulous observation, the objects that I represent are unique to the hand and cannot be replicated in any other way. I encourage my audience to find their own method of experiencing their environment through the use of their hands
Pivot-Point Procedures in Practical Travel Demand Forecasting
For many cities, regions and countries, large-scale model systems have been developed to support the development of transport policy. These models are intended to predict the traffic flows that are likely to result from assumed exogenous developments and transport policies affecting people and businesses in the relevant area. The accuracy of the model is crucial to determining the quality of the information that can be extracted as input to the planning and policy analysis process. A frequent approach to modelling, which can substantially enhance the accuracy of the model, is to formulate the model as predicting changes relative to a base-year situation. Often, base-year traffic flows can be observed rather accurately and the restriction of the model to predicting differences reduces the scope for errors in the modelling â whether they be caused by errors in the model itself or in the inputs to the model â to influence the outputs. Such approaches are called âpivot pointâ methods, or sometimes incremental models. The approaches have proved themselves beneficial in practical planning situations and now form part of the recommended âVaDMAâ (Variable Demand Modelling Advice) guidelines issued by the UK Department for Transport. While the principle of the pivot point is clear, the implementation of the principle in practical model systems can be done in a number of ways and the choice between these can have substantial influence on the model forecasts. In particular modellers need to consider: 1.whether the change predicted by the model should be expressed as an absolute difference or a proportional ratio, or whether a mixed approach is necessary; 2.how to deal with apparently growth in âgreen-fieldâ situations when applying these approaches; 3,at what level in the model should the pivoting apply, i.e. at the level of mode choice, destination choice, overall travel frequency or combinations of these; 4,whether the pivoting is best undertaken as an operation conducted on a âbase matrixâ or the model is constructed so that it automatically reproduces the base year situation with base year inputs. The paper reviews the alternative approaches to each of these issues, discussing current practice and attempting to establish the basis on which alternative approaches might be established; in particular, whether pivoting is treated as a correction to a model which is in principle correctly specified but incorporates some error, perhaps from faulty data, or as a partial replacement for a model that handles at best part of the situation. These views of the pivoting lead to different procedures. It goes on to present and justify the approach that the authors have found useful in a number of large-scale modelling studies in The Netherlands, the United Kingdom and elsewhere, pointing out the problems that have led to the calculations that are recommended.
How Working age People with Disabilities Fared over the 1990s Business Cycle
Using data from the March Current Population Survey (CPS) we show that while the longest peacetime economic expansion in United States history has increased the economic well-being of most Americans, the majority of working age men and women with disabilities have been left behind. Robust economic growth since the recession of the early 1990s has lifted nearly all percentiles of the income distribution of working age men and men without disabilities beyond their previous business cycle peak levels of 1989. In contrast, the majority of working age men and women with disabilities did not share in economic growth over this period. Not only did their employment and labor earnings fall during the recession of the early 1990s but their employment and earnings continued to fall during the economic expansion that followed
Economics of Disability Research Report #5: Economic Outcomes of Working-Age People with Disabilities over the Business Cycle â an Examination of the 1980s and 1990s
We examine the rate of employment and the household income of the working-age population (aged 25-61) with and without disabilities over the business cycles of the 1980s and 1990s using data from the March Current Population Survey and the National Health Interview Survey. In general, we find that while the employment of working-age men and women with and without disabilities exhibited a procyclical trend during the 1980s business cycle, this was not the case during the 1990s expansion. During the 1990s, the employment of working-age men and women without disabilities continued to be procyclical, but the employment rates of their counterparts with disabilities declined over the entire 1990s business cycle. Although increases in disability transfer income replaced a significant fraction of their lost earnings, the household income of men and women with disabilities fell relative to the rest of the population over the decade
A Compositional Investigation into Style and Genre Fusion Utilising Popular Electronic and Alternative Rock Music
The purpose of this study is to find out the limitations of style and genre fusion. It asks how effectively can a composer achieve this This thesis explores the restrictions of the ideas of style and genre fusion by examining if one genre will overpower the other in terms of its sonic signature and social ideals or if a balanced fusion can be achieved? Another question of interest, is how far apart can two fusions by the same composer of the same two genres stylistically be from one another? The study consists of a portfolio of compositions that explore the subject and his accompanying thesis will discuss the research that informed them as well as some discussion of the compositions themselves
Arendt and Christianity: On Love and the World
Hannah Arendt criticized the Christian faith for what she saw as an inherent wordlessness or ascetic attitude. She believed this focus on the afterlife was an afront to her political philosophy and kept people from participating in the public sphere. This thesis is a selective exploration of Arendtâs criticisms against the Christian faith and aims to show that there is a way of reconciling the respective belief systems, allowing an Arendtian to benefit from Christian ideas and a Christian to improve themselves with the assistance of Arendtian concepts. The project is split into two chapters. Each chapter focuses on a point of comparison and tries to show how each side views the point before concluding that reconciliation is possible between the two parties. The first chapter addresses Arendt\u27s main concern about the world and the Christian attitude of contemptus mundi. It makes the case that Arendt was wrong to say that Christianity is necessarily and inherently worldless, and that Christians ought to listen to Arendt\u27s call to be active participants in the world. The second chapter wrestles with Arendt\u27s concept of love. She believed love to be problematic for politics but seems to also say it is a necessary part of the proper attitude toward the world. This chapter aims to show that Arendt was wrong in her dismissal of love and that her philosophy is enhanced by the Christian faith\u27s focus on love as the ultimate fulfillment of the Law
Self-Reported Work Limitation Data: What They Can and Cannot Tell Us
Data constraints make the long-term monitoring of the working-age population with disabilities a difficult task. Indeed, the Current Population Survey (CPS) is the only national data source that offers detailed work and income questions and consistently asked measures of disability over a 20-year period. Despite its widespread use in the literature, the CPS and surveys like it have come under attack of late, with critics discounting the results of any research obtained from such data. We put these criticisms in perspective by systematically examining what the CPS data can and cannot be used for in disability research. Based on comparisons with the National Health Interview Survey (NHIS), a data set with much more information on health than the CPS, we find that the work limitation-based definition of disability available in the CPS underestimates the size of the broader population with health impairments in the NHIS, but that the employment trends in these two populations in the NHIS are not significantly different from one another. We then show that the trends in employment observed for the NHIS population defined by self-reported work limitation are not statistically different from those found in the CPS. Based on these findings, we argue (1) that the CPS and other nationally representative employment-based data sets can be used to monitor trends in outcomes of those with disabilities and, (2) that the dramatic decline in the employment of people with disabilities we describe in the CPS during the 1990s is not an artifact of the data
Modelling departure time and mode choice
As a result of increasing road congestion and road pricing, modelling the temporal response of travellers to transport policy interventions has rapidly emerged as a major issue in many practical transport planning studies. A substantial body of research is therefore being carried out to understand the complexities involved in modelling time of day choice. These models are contributing substantially to our understanding of how travellers make time-of-day decisions (Hess et al, 2004; de Jong et al, 2003). These models, however, tend to be far too complex and far too data intensive to be of use for application in large-scale modelling forecasting systems, where socio-economic detail is limited and detailed scheduling information is rarely available. Moreover, model systems making use of the some of the latest analytical structures, such as Mixed Logit, are generally inapplicable in practical planning, since they rely on computer-intensive simulation in application just as well as in estimation. The aim of this paper, therefore, is to describe the development of time-period choice models which are suitable for application in large-scale modelling forecasting systems. Large-scale practical planning models often rely on systems of nested logit models, which can incorporate many of the most important interactions that are present in the complex models but which have low enough run-times to allow them to be used for practical planning. In these systems, temporal choice is represented as the choice between a finite set of discrete alternatives, represented by mutually exclusive time-periods that are obtained by aggregation of the actual observed continuous time values. The issues that face modellers are then: -how should the time periods be defined, and in particular how long should they be? -how should the choices of time periods be related to each other, e.g. is the elasticity for shorter shifts greater than for longer shifts? -how should time period choice be placed in the model system relative to other choices, such as that of the mode of travel? These questions cannot be answered on a purely theoretical basis but require the analysis of empirical data. However, there is not a great deal of data available on the relevant choices. The time period models described in the paper are developed from three related stated preference (SP) studies undertaken over the past decade in the United Kingdom and the Netherlands. Because of the complications involved with using advanced models in large-scale modelling forecasting systems, the model structures are limited to nested logit models. Two different tree structures are explored in the analysis, nesting mode above time period choice or time period choice above mode. The analysis examines how these structures differ by data set, purpose of travel and time period specification. Three time period specifications were tested, dividing the 24-hour day into: -twenty-four 1-hour periods; -five coarse time-periods; -sixteen 15-minute morning-peak periods, and two coarse pre-peak and post-peak periods. In each case, the time periods are used to define both the outbound and the return trip timings. The analysis shows that, with a few exceptions, the nested models outperform the basic Multinomial Logit structures, which operate under the assumption of equal substitution patterns across alternatives. With a single exception, the nested models in turn show higher substitution between alternative time periods than between alternative modes, showing that, for all the time period lengths studied, travellers are more sensitive to transport levels of service in their choice of departure time than in choice of mode. The advantages of the nesting structures are especially pronounced in the 1-hour and 15-minute models, while, in the coarse time-period models, the MNL model often remains the preferred structure; this is a clear effect of the broader time-periods, and the consequently lower substitution between time-periods.
The happiness - suicide paradox
Suicide is an important scientific phenomenon. Yet its causes remain poorly understood. This study documents a paradox: the happiest places have the highest suicide rates. The study combines findings from two large and rich individual-level data setsâone on life satisfaction and another on suicide deathsâto establish the paradox in a consistent way across U.S. states. It replicates the finding in data on Western industrialized nations and checks that the paradox is not an artifact of population composition or confounding factors. The study concludes with the conjecture that people may find it particularly painful to be unhappy in a happy place, so that the decision to commit suicide is influenced by relative comparisons.Happiness ; Suicide
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