Using problem-based learning for introducing producer theory and market structure in intermediate microeconomics

This paper shows how instructors can use the problem‐based learning method to introduce producer theory and market structure in intermediate microeconomics courses. The paper proposes a framework where different decision problems are presented to students, who are asked to imagine that they are the managers of a firm who need to solve a problem in a particular business setting. In this setting, the instructors’ role isto provide both guidance to facilitate student learning and content knowledge on a just‐in‐time basis

Effects of brood manipulation costs on optimal sex allocation in social hymenoptera.

In eusocial Hymenoptera, queens and workers are in conflict over optimal sex allocation. Sex ratio theory, while generating predictions on the extent of this conflict under a wide range of conditions, has largely neglected the fact that worker control of investment almost certainly requires the manipulation of brood sex ratio. This manipulation is likely to incur costs, for example, if workers eliminate male larvae or rear more females as sexuals rather than workers. In this article, we present a model of sex ratio evolution under worker control that incorporates costs of brood manipulation. We assume cost to be a continuous, increasing function of the magnitude of sex ratio manipulation. We demonstrate that costs counterselect sex ratio biasing, which leads to less female-biased population sex ratios than expected on the basis of relatedness asymmetry. Furthermore, differently shaped cost functions lead to different equilibria of manipulation at the colony level. While linear and accelerating cost functions generate monomorphic equilibria, decelerating costs lead to a process of evolutionary branching and hence split sex ratios.

Analyzing shapes as compositions of distances

We propose to analyze shapes as “compositions” of distances in Aitchison geometry asan alternate and complementary tool to classical shape analysis, especially when sizeis non-informative.Shapes are typically described by the location of user-chosen landmarks. Howeverthe shape – considered as invariant under scaling, translation, mirroring and rotation– does not uniquely define the location of landmarks. A simple approach is to usedistances of landmarks instead of the locations of landmarks them self. Distances arepositive numbers defined up to joint scaling, a mathematical structure quite similar tocompositions. The shape fixes only ratios of distances. Perturbations correspond torelative changes of the size of subshapes and of aspect ratios. The power transformincreases the expression of the shape by increasing distance ratios. In analogy to thesubcompositional consistency, results should not depend too much on the choice ofdistances, because different subsets of the pairwise distances of landmarks uniquelydefine the shape.Various compositional analysis tools can be applied to sets of distances directly or afterminor modifications concerning the singularity of the covariance matrix and yield resultswith direct interpretations in terms of shape changes. The remaining problem isthat not all sets of distances correspond to a valid shape. Nevertheless interpolated orpredicted shapes can be backtransformated by multidimensional scaling (when all pairwisedistances are used) or free geodetic adjustment (when sufficiently many distancesare used)

A Bayesian network approach to the database serch problem in criminal proceedings

Background The 'database search problem', that is, the strengthening of a case - in terms of probative value - against an individual who is found as a result of a database search, has been approached during the last two decades with substantial mathematical analyses, accompanied by lively debate and centrally opposing conclusions. This represents a challenging obstacle in teaching but also hinders a balanced and coherent discussion of the topic within the wider scientific and legal community. This paper revisits and tracks the associated mathematical analyses in terms of Bayesian networks. Their derivation and discussion for capturing probabilistic arguments that explain the database search problem are outlined in detail. The resulting Bayesian networks offer a distinct view on the main debated issues, along with further clarity. Methods As a general framework for representing and analyzing formal arguments in probabilistic reasoning about uncertain target propositions (that is, whether or not a given individual is the source of a crime stain), this paper relies on graphical probability models, in particular, Bayesian networks. This graphical probability modeling approach is used to capture, within a single model, a series of key variables, such as the number of individuals in a database, the size of the population of potential crime stain sources, and the rarity of the corresponding analytical characteristics in a relevant population. Results This paper demonstrates the feasibility of deriving Bayesian network structures for analyzing, representing, and tracking the database search problem. The output of the proposed models can be shown to agree with existing but exclusively formulaic approaches. Conclusions The proposed Bayesian networks allow one to capture and analyze the currently most well-supported but reputedly counter-intuitive and difficult solution to the database search problem in a way that goes beyond the traditional, purely formulaic expressions. The method's graphical environment, along with its computational and probabilistic architectures, represents a rich package that offers analysts and discussants with additional modes of interaction, concise representation, and coherent communication.

Resource dimensioning aspect of heterogeneous traffic with different service requirements: Integration versus segregation

In this paper, we consider the ATM networks in which the virtual path concept is implemented. The question of how to multiplex two or more diverse traffic classes while providing different quality of service requirements is a very complicated open problem. Two distinct options are available: integration and segregation. In an integration approach all the traffic from different connections are multiplexed onto one VP. This implies that the most restrictive QOS requirements must be applied to all services. Therefore, link utilization will be decreased because unnecessarily stringent QOS is provided to all connections. With the segregation approach the problem can be much simplified if different types of traffic are separated by assigning a VP with dedicated resources (buffers and links). Therefore, resources may not be efficiently utilized because no sharing of bandwidth can take place across the VP. The probability that the bandwidth required by the accepted connections exceeds the capacity of the link is evaluated with the probability of congestion (PC). Since the PC can be expressed as the CLP, we shall simply carry out bandwidth allocation using the PC. We first focus on the influence of some parameters (CLP, bit rate and burstiness) on the capacity required by a VP supporting a single traffic class using the new convolution approach. Numerical results are presented both to compare the required capacity and to observe which conditions under each approach are preferred

Alternative ways to estimate change points in multinomial sequences. An application to an authorship attribution problem

The statistical analysis of literary style is the part of stylometry that compares measurable characteristicsin a text that are rarely controlled by the author, with those in other texts. When thegoal is to settle authorship questions, these characteristics should relate to the author’s style andnot to the genre, epoch or editor, and they should be such that their variation between authors islarger than the variation within comparable texts from the same author.For an overview of the literature on stylometry and some of the techniques involved, see for exampleMosteller and Wallace (1964, 82), Herdan (1964), Morton (1978), Holmes (1985), Oakes (1998) orLebart, Salem and Berry (1998).Tirant lo Blanc, a chivalry book, is the main work in catalan literature and it was hailed to be“the best book of its kind in the world” by Cervantes in Don Quixote. Considered by writterslike Vargas Llosa or Damaso Alonso to be the first modern novel in Europe, it has been translatedseveral times into Spanish, Italian and French, with modern English translations by Rosenthal(1996) and La Fontaine (1993). The main body of this book was written between 1460 and 1465,but it was not printed until 1490.There is an intense and long lasting debate around its authorship sprouting from its first edition,where its introduction states that the whole book is the work of Martorell (1413?-1468), while atthe end it is stated that the last one fourth of the book is by Galba (?-1490), after the death ofMartorell. Some of the authors that support the theory of single authorship are Riquer (1990),Chiner (1993) and Badia (1993), while some of those supporting the double authorship are Riquer(1947), Coromines (1956) and Ferrando (1995). For an overview of this debate, see Riquer (1990).Neither of the two candidate authors left any text comparable to the one under study, and thereforediscriminant analysis can not be used to help classify chapters by author. By using sample textsencompassing about ten percent of the book, and looking at word length and at the use of 44conjunctions, prepositions and articles, Ginebra and Cabos (1998) detect heterogeneities that mightindicate the existence of two authors. By analyzing the diversity of the vocabulary, Riba andGinebra (2000) estimates that stylistic boundary to be near chapter 383.Following the lead of the extensive literature, this paper looks into word length, the use of the mostfrequent words and into the use of vowels in each chapter of the book. Given that the featuresselected are categorical, that leads to three contingency tables of ordered rows and therefore tothree sequences of multinomial observations.Section 2 explores these sequences graphically, observing a clear shift in their distribution. Section 3describes the problem of the estimation of a suden change-point in those sequences, in the followingsections we propose various ways to estimate change-points in multinomial sequences; the methodin section 4 involves fitting models for polytomous data, the one in Section 5 fits gamma modelsonto the sequence of Chi-square distances between each row profiles and the average profile, theone in Section 6 fits models onto the sequence of values taken by the first component of thecorrespondence analysis as well as onto sequences of other summary measures like the averageword length. In Section 7 we fit models onto the marginal binomial sequences to identify thefeatures that distinguish the chapters before and after that boundary. Most methods rely heavilyon the use of generalized linear models

A survey addressing the fundamental matrix estimation problem

Epipolar geometry is a key point in computer vision and the fundamental matrix estimation is the only way to compute it. This article surveys several methods of fundamental matrix estimation which have been classified into linear methods, iterative methods and robust methods. All of these methods have been programmed and their accuracy analysed using real images. A summary, accompanied with experimental results, is given

Thickening of the skin on the forehead: a quiz. Acanthosis nigricans with forehead location.

Publicado en la Sección Quiz de la revista.

Epileptogenic zone, electrode location and clinical outcome in hippocampal electrical stimulation for mesial temporal lobe epilepsy : a correlation study

Objectif : Etudier les résultats cliniques du traitement de patients atteints pai- une épilepsie mésiale du lobe temporal (MTLE) réfractaire, par stimulation cérébrale profonde (DBS) de l'hippocampe, en fonction de l'emplacement de l'électrode. Méthodes : Huit patients atteints de MTLE implantés dans l'hippocampe et stimulés par DBS à haute fréquence ont été inclus dans cette étude. Cinq ont subi des enregistrements invasifs avec des électrodes profondes dans le but d'estimer la localisation du foyer ictal avant de procéder à une DBS chronique. La position des contacts actifs de l'électrode a été mesurée en utilisant une imagerie post-opératoire. Les distances par rapport au foyer ictal ont été calculées, et les structures hippocampiques influencées par la stimulation ont été identifiées au moyen d'un atlas neuro-anatomique. Ces deux paramètres ont été corrélés avec la réduction de la fréquence d'apparition des crises. Résultats : Les distances entre la localisation estimée des contacts actifs de l'électrode et le foyer ictal étaient respectivement 11.0 +/- 4.3 ou 9.1 +/- 2.3 mm pour les patients présentant une réduction de > 50% ou < 50% de la fréquence des crises. Chez les patients (N = 6) montrant une réduction de > 50% de la fréquence des crises, 100% avaient des contacts actifs situés à < 3 mm du subiculum (p < 0,05). Les 2 patients ne répondant pas au traitement étaient stimulés par des contacts situés à > 3mm du subiculum. Conclusion : La diminution de l'activité épileptogène induite par DBS sur l'hippocampe dans les cas de MTLE réfractaires : 1) ne semble pas directement liée à la proximité des contacts actifs de l'électrode au foyer ictal déterminé par les enregistrements invasifs ; 2) pourrait être obtenue par une neuro-modulation du subiculum.

Reproductive allocation strategies: a long-term study on proximate factors and temporal adjustments in a viviparous lizard.

Optimisation of reproductive investment is crucial for Darwinian fitness, and detailed long-term studies are especially suited to unravel reproductive allocation strategies. Allocation strategies depend on the timing of resource acquisition, the timing of resource allocation, and trade-offs between different life-history traits. A distinction can be made between capital breeders that fuel reproduction with stored resources and income breeders that use recently acquired resources. In capital breeders, but not in income breeders, energy allocation may be decoupled from energy acquisition. Here, we tested the influence of extrinsic (weather conditions) and intrinsic (female characteristics) factors during energy storage, vitellogenesis and early gestation on reproductive investment, including litter mass, litter size, offspring mass and the litter size and offspring mass trade-off. We used data from a long-term study of the viviparous lizard, Lacerta (Zootoca) vivipara. In terms of extrinsic factors, rainfall during vitellogenesis was positively correlated with litter size and mass, but temperature did not affect reproductive investment. With respect to intrinsic factors, litter size and mass were positively correlated with current body size and postpartum body condition of the previous year, but negatively with parturition date of the previous year. Offspring mass was negatively correlated with litter size, and the strength of this trade-off decreased with the degree of individual variation in resource acquisition, which confirms theoretical predictions. The combined effects of past intrinsic factors and current weather conditions suggest that common lizards combine both recently acquired and stored resources to fuel reproduction. The effect of past energy store points out a trade-off between current and future reproduction.

Topics in public finance: social security and taxation

Summary The field of public finance focuses on the spending and taxing activities of governments and their influence on the allocation of resources and distribution of income. This work covers in three parts different topics related to public finance which are currently widely discussed in media and politics. The first two parts deal with issues on social security, which is in general one of the biggest spending shares of governments. The third part looks at the main income source of governments by analyzing the perceived value of tax competition. Part one deals with the current problem of increased early retirement by focusing on Switzerland as a special case. Early retirement is predominantly considered to be the result of incentives set by social security and the tax system. But the Swiss example demonstrates that the incidence of early retirement has dramatically increased even in the absence of institutional changes. We argue that the wealth effect also plays an important role in the retirement decision for middle and high income earners. An actuarially fair, but mandatory funded system with a relatively high replacement rate may thus contribute to a low labor market participation rate of elderly workers. We provide evidence using a unique dataset on individual retirement decisions in Swiss pension funds, allowing us to perfectly control for pension scheme details. Our findings suggest that affordability is a key determinant in the retirement decisions. The higher the accumulated pension capital, the earlier men, and to a smaller extent women, tend to leave the workforce. The fact that early retirement has become much more prevalent in the last 15 years is a further indicator of the importance of a wealth effect, as the maturing of the Swiss mandatory funded pension system over that period has led to an increase in the effective replacement rates for middle and high income earners. Part two covers the theoretical side of social security. Theories analyzing optimal social security benefits provide important qualitative results, by mainly using one general type of an economy. Economies are however very diverse concerning numerous aspects, one of the most important being the wealth level. This can lead to significant quantitative benefit differences that imply differences in replacement rates and levels of labor supply. We focus on several aspects related to this fact. In a within cohort social security model, we introduce disability insurance with an imperfect screening mechanism. We then vary the wealth level of the model economy and analyze how the optimal social security benefit structure or equivalently, the optimal replacement rates, changes depending on the wealth level of the economy, and if the introduction of disability insurance into a social security system is preferable for all economies. Second, the screening mechanism of disability insurance and the threshold level at which people are defined as disabled can differ. For economies with different wealth levels, we determine for different thresholds the screening level that maximizes social welfare. Finally, part three turns to the income of governments, by adding an element to the controversy on tax competition versus tax harmonization.2 Inter-jurisdictional tax competition can generate at least two potential benefits or costs: On a public level, tax competition may result in a lower or higher efficiency in the production of public services. But there is also a more private benefit in the form of an option for individuals to move to a community with a lower tax rate in the future. To explore the value citizens attach to tax competition we analyze a unique popular vote for a complete tax harmonization between communities in the third largest Swiss canton, Vaud. Although a majority of voters would have seemingly benefited from replacing the current tax rate by a revenue-neutral average tax rate, the proposal was rejected by a large margin. Our estimates suggest that the estimated combined perceived benefit from tax competition is in the range of 10%.