Introducing a general class of species diversification models for phylogenetic trees

Phylogenetic trees are types of networks that describe the temporal relationship between individuals, species, or other units that are subject to evolutionary diversification. Many phylogenetic trees are constructed from molecular data that is often only available for extant species, and hence they lack all or some of the branches that did not make it into the present. This feature makes inference on the diversification process challenging. For relatively simple diversification models, analytical or numerical methods to compute the likelihood exist, but these do not work for more realistic models in which the likelihood depends on properties of the missing lineages. In this article, we study a general class of species diversification models, and we provide an expectation-maximization framework in combination with a uniform sampling scheme to perform maximum likelihood estimation of the parameters of the diversification process.     

Are specific skills an obstacle to labor market adjustment?

This paper shows that specialized education reduces workers’ mobility and hence their ability to cope with economic changes. We illustrate this point using labor force data from two countries having experienced important macroeconomic turbulence; a large economy with rigid labor markets, Poland, and a small open economy with increased flexibility, Estonia. We find that holding a vocational degree is associated with much longer unemployment duration spells and higher likelihood of leaving activity for older workers. We then build a theoretical framework in which young agents’ careers are heavily determined by the type of initial education, and analyze the transition to a new steady-state after a sectoral demand shift. Quantitative exercises suggest that the over-specialization of the labor force in Poland led to much higher and persistent unemployment compared to Estonia during the period of EU enlargement. Traditional labor market institutions (wage rigidity and employment protection) lead to an increase of the unemployment gap, but to a lesser extent.     

Credibility in Favor of Unlucky Insureds

Abstract

The classical Bühlmann credibility formula estimates the hypothetical mean of a particular insured, or risk, by a weighted average of the grand mean of the collection of risks with the sample mean of the given insured. If the insured is unfortunate enough to have had large claims in the previous policy period(s), then the estimate of future claims for that risk will also be large. In this paper we provide actuaries with a method for not overly penalizing an unlucky insured while still targeting the goal of accuracy in the estimate. We propose a credibility estimator that minimizes the expectation of a linear combination of a squared-error term and a first-derivative term. The squared-error term measures the accuracy of the estimator, while the first-derivative term constrains the estimator to be close to constant.     

An Incomplete Contract Perspective on Public Good Provision

Abstract.  This paper surveys what can be learned from recent advances in the incomplete contract literature to understand how public goods are or should be provided. The paper starts with a section on the full information case that presents and discusses the classical Samuelson condition on the optimal provision of public goods. The rest of the paper presents results under asymmetric information. It is constituted of two main parts. In the first one, the social planner has complete contracting ability. We discuss the basic setting and assumptions of this comprehensive contracting approach and study the trade-offs it generates. The second part of the paper is devoted to the study of contracting incompleteness. Such incompleteness can emerge from various sources, which we present and discuss. We then study the case of a politically chosen decision-maker and the consequences of its inability to commit for more than one period and of the ability for individuals to form groups. Finally, we address the problem of the choice between public and private forms of public good provision. The concluding section summarizes the main policy lessons.     

Towards unveiling individual differences in different stages of information processing: a clustering-based approach

Information Integration Theory (IIT) is a theory of judgment in daily life. Its principal aim is to study the cognitive rules that people use to integrate information when they make a judgment. Traditionally, the identification of individual differences in these qualitatively different integration rules requires individual designs. It also requires the grouping of individuals according to their integration rule, which can be a challenging task, particularly when the data are noisy or when the pattern involves many factors. This paper builds on the cluster analysis tradition for developing a series of clustering procedures that can be implemented for studying, not only individual differences in integration rules, but also individual differences in other stages of information processing. These procedures are intended to simplify the identification of differences in (a) the subjective valuation of information, (b) the integration of the subjective values, and (c) general attitudes before judging.     

How efficient is maize production among smallholder farmers in Zimbabwe? A comparison of semiparametric and parametric frontier efficiency analyses

The controversial Fast Track Land Reform Programme in Zimbabwe that redistributes commercially-owned farmland to smallholder households has caused concerns about the efficiency of agricultural production in the country. In this paper, we estimate the efficiency of resource use among smallholder farmers in Zimbabwe when producing maize, the staple crop in the country. Using both a semiparametric model and a fully parametric stochastic frontier model, we find significant production shortfalls for smallholder maize production. While labor, capital, and land all significantly affect the total output, the estimated mean efficiency score for farms with less than 10 hectares of land (A1) appears to be under 0.75, and for the entire sample (A1 and A2) it ranges between 0.595 and 0.772. There clearly exists a great potential for maize farmers to improve the technical efficiency and increase the total output. Gender and age of the household head, access to extension services, and activities of other crops significantly affect the technical efficiency of smallholder maize production in Zimbabwe. We also find that all farms operate under increasing returns to scale and that the technical efficiency score tends to increase with the level of output.     

A THEORY OF WAGES AND LABOR DEMAND WITH INTRA‐FIRM BARGAINING AND MATCHING FRICTIONS*

This article provides a model of labor market equilibrium with search and within‐firm strategic bargaining. We yield explicit closed form solutions with heterogeneous labor inputs and capital. The solution exhibits overemployment. We show that higher relative bargaining power for some groups of workers may lead to overemployment relative to other groups, with such other groups being underemployed instead if they have a lower relative bargaining power. Similarly, the hold‐up problem between capitalists and employees does not necessarily lead to underinvestment in physical capital.     

An introduction to the special feature section: Price,wage and employment adjustments in 2007–2008 and some inference for the current European crisis

The four papers in this issue are part of a collective effort coordinated by the ECB and European National Central Banks, the Eurosystem's Wage Dynamics Network Survey. They provide new and systematic evidence on wage and price flexibility in Europe and attempt to explain their determinants.     

Housing and the labor market: Time to move and aggregate unemployment

Conventional macro-search models (Mortensen and Pissarides) with unemployment benefits and taxes have been able to account for the variation in unemployment rates across countries but do not account for the role geographic mobility or commuting time might play. We build a model in which both unemployment and mobility rates are endogenous. Our findings indicate that an increase in unemployment benefits and in taxes does not generate a strong decline in mobility but does increase unemployment as in the standard model. We find that with higher commuting costs the effect of housing frictions plays a large role and can generate a substantial decline in mobility.