Search results for "CONTRAST"

The effect of predator appetite, prey warning coloration and luminance on predator foraging decisions

2010

AbstractAposematic prey advertise their defence to visually hunting predators using conspicuous warning colouration. Established theory predicts that aposematic signals should evolve towards increased conspicuousness and similarity to enhance predator education. Contrary to theoretical expectations, there is often considerable within- and between-species variation in aposematic signals of animals sharing the same ecological niche, phylogeny and predators. This may be explained by varying responses of predators that weaken the selection pressure for a consistent signal. By presenting painted mealworm larvae as prey to great tits as predators we tested if different aposematic colour patterns …

Weak versus strong dominance of shrinkage estimators

2021

We consider the estimation of the mean of a multivariate normal distribution with known variance. Most studies consider the risk of competing estimators, that is the trace of the mean squared error matrix. In contrast we consider the whole mean squared error matrix, in particular its eigenvalues. We prove that there are only two distinct eigenvalues and apply our findings to the James–Stein and the Thompson class of estimators. It turns out that the famous Stein paradox is no longer a paradox when we consider the whole mean squared error matrix rather than only its trace.

Institutions and geography: Empirical test of spatial growth models for European regions

2010

Abstract This article provides an empirical assessment of the growth experiences of European regions, during the period 1991–2004, by taking into account the spatial effects due to both institutions and geography. These effects have been modelled by means of specific controls and by using a non-conventional spatial weight matrix. Results favour a model dealing with substantive spatial externalities. Within this framework, the country-specific institutions are strongly and positively related to the regional productivity's growth rate. In addition, the geo-institutional proximity increases the spatial dependence of the regional output per worker and raises the speed of convergence. By contras…

Do Scarring Effects of Low-Wage Employment and Non-Employment Differ BETWEEN Levels of Qualification?

2014

This study investigates how the effects of low-wage employment and non-employment on wage prospects vary depending on qualification. Based on theories on signalling effects, human capital and job search, we discuss why there may be heterogeneity in state dependence in both labour market states. We find that episodes of low-wage employment incur a significantly lower risk of future non-employment than episodes of non-employment for low-qualified workers. In contrast, for workers with a middle or high level of qualification the risk of non-employment is not significantly different when being low-paid instead of not employed.

Job Mobility and Sorting: Theory and Evidence

2019

Abstract Motivated by the canonical (random) on-the-job search model, I measure a person’s ability to sort into higher ranked jobs by the risk ratio of job-to-job transitions to transitions into unemployment. I show that this measure possesses various desirable features. Making use of the Survey of Income and Program Participation (SIPP), I study the relation between human capital and the risk ratio of job-to-job transitions to transitions into unemployment. Formal education tends to be positively associated with this risk ratio. General experience and occupational tenure have a pronounced negative correlation with both job-to-job transitions and transitions into unemployment, leaving the r…

A Test of Covariance-Matrix Forecasting Methods

2015

Providing a more accurate covariance matrix forecast can substantially improve the performance of optimized portfolios. Using out-of-sample tests, in this article the author evaluates alternative covariance matrix-forecasting methods by looking at: (1) their forecast accuracy, (2) their ability to track the volatility of a minimum-variance portfolio, and (3) their ability to keep the volatility of a minimum-variance portfolio at a target level. The author finds large differences between the methods. The results suggest that shrinking the sample covariance matrix improves neither the forecast accuracy nor the performance of minimum-variance portfolios. In contrast, switching from the sample …

Special functions for the study of economic dynamics: The case of the Lucas-Uzawa model

2008

The special functions are intensively used in mathematical physics to solve differential systems. We argue that they should be most useful in economic dynamics, notably in the assessment of the transition dynamics of endogenous economic growth models. We illustrate our argument on the famous Lucas-Uzawa model, which we solve by the means of Gaussian hypergeometric functions. We show how the use of Gaussian hypergeometric functions allows for an explicit representation of the equilibrium dynamics of all variables in level. The parameters of the involved hypergeometric functions are identified using the Pontryagin conditions arising from the underlying optimization problems. In contrast to th…

On the drivers of successful crowdfunding: The case of the platform Verkami

2021

This article analyzes the determinants of successful crowdfunding initiatives using a sample of 5,251 projects from the reward-based Spanish platform Verkami. In contrast to most of the literature that has measured success with a dichotomous variable, we approach success with a continuous one, namely the ratio of achievement, which is measured as the obtained resources over the total amount requested by the promoter. We consider a set of potential determinants of success, which are theoretically well-grounded and cover a variety of spheres related to project features. Results suggest that factors related to the signaling theories such as partnership, having previous experience and interact…

2012

BackgroundIncreased reaction time variability (RTV) on cognitive tasks requiring a speeded response is characteristic of several psychiatric disorders. In attention deficit hyperactivity disorder (ADHD), the association with RTV is strong phenotypically and genetically, yet high RTV is not a stable impairment but shows ADHD-sensitive improvement under certain conditions, such as those with rewards. The state regulation theory proposed that the RTV difference score, which captures change from baseline to a rewarded or fast condition, specifically measures ‘state regulation’. By contrast, the interpretation of RTV baseline (slow, unrewarded) scores is debated. We aimed to investigate directly…

Corpus linguistics and its aplications in higher education

2010

The aim of this paper is to review and analyse relevant factors related to the implementation of corpus linguistics (CL) in higher education. First we set out to describe underlying principles of CL and its developments in relation to theoretical linguistics and its applications in modern teaching practices. Then we attempt to establish how different types of corpora have contributed to the development of direct and indirect approaches in language teaching. We single out Data Driven Learning (DDL) due to its relevance in applied linguistics literature, and examine in detail advantages and drawbacks. Finally, we outline problems concerning the implementation of CL in the classroom since awar…