Estimation of Conditional Ranks and Tests of Exogeneity in Nonparametric Nonseparable Models

Consider a nonparametric nonseparable regression model Y = ?(Z, U), where ?(Z, U) is strictly increasing in U and U ～ U[0, 1]. We suppose that there exists an instrument W that is independent of U. The observable random variables are Y, Z, and W, all one-dimensional. We construct test statistics for the hypothesis that Z is exogenous, that is, that U is independent of Z. The test statistics are based on the observation that Z is exogenous if and only if V = F_Y|Z(Y|Z) is independent of W, and hence they do not require the estimation of the function ?. The asymptotic properties of the proposed tests are proved, and a bootstrap approximation of the critical values of the tests is shown to be consistent and to work for finite samples via simulations. An empirical example using the U.K. Family Expenditure Survey is also given. As a byproduct of our results we obtain the asymptotic properties of a kernel estimator of the distribution of V, which equals U when Z is exogenous. We show that this estimator converges to the uniform distribution at faster rate than the parametric n^{? 1/2}-rate.     

From Linear to Semidefinite Programming: An Algorithm to Obtain Semidefinite Relaxations for Bivalent Quadratic Problems

In this paper, we present a simple algorithm to obtain mechanically SDP relaxations for any quadratic or linear program with bivalent variables, starting from an existing linear relaxation of the considered combinatorial problem. A significant advantage of our approach is that we obtain an improvement on the linear relaxation we start from. Moreover, we can take into account all the existing theoretical and practical experience accumulated in the linear approach. After presenting the rules to treat each type of constraint, we describe our algorithm, and then apply it to obtain semidefinite relaxations for three classical combinatorial problems: the K-CLUSTER problem, the Quadratic Assignment Problem, and the Constrained-Memory Allocation Problem. We show that we obtain better SDP relaxations than the previous ones, and we report computational experiments for the three problems.     

Sex and cultural differences in the acceptance of functional foods: a comparison of American, Canadian, and French college students

OBJECTIVE: Functional foods (FF)--foods containing nutritional supplements in addition to natural nutrients--have an increasing presence in the marketplace. Expanding on previous research, the authors investigated college students' acceptance of FF. PARTICIPANTS: In September--March 2004, 811 undergraduates in Canada, the United States, and France participated in the study. METHODS: A self-administered questionnaire measured students' general food attitudes and beliefs as well as FF-related knowledge, attitudes, beliefs, and purchase intention. RESULTS: Overall, participants slightly favored FF over traditional foods. However, although most respondents associated FF with positive health benefits, many remained dubious of currently available FF information. In terms of culture and sex, the authors found small but significant divergences in FF knowledge, attitudes, and behaviors. CONCLUSIONS: Stronger labeling and education efforts may increase cross-cultural acceptance of FF by college students.     

Incremental exercise tests in master athletes and untrained older adults

This study aimed to analyze the impact of step-duration protocols, 1-min vs. 3-min, on cardiorespiratory responses to exercise, whatever the aerobic-fitness level of sedentary (65.5 +/- 2.3 years, n = 8) or highly fit (63.1 +/- 3.2 years, n = 19) participants. Heart rate and VO2 at the first and second ventilatory thresholds (VT1 ,VT2) and maximal exercise were not significantly different between the two protocols. In master athletes, the 3-min protocol elicited significantly lower ventilation at VT2 and maximal exercise (p < .01). In the latter, breathlessness was also lower at maximal exercise (p < .05) than in sedentary participants. In trained or sedentary older adults, VT1, VT2, and were not influenced by stage duration. According to the lower breathlessness and ventilation, however, the 3-min step protocol could be more appropriate in master athletes. In untrained participants, because the cardiorespiratory responses were similar with the two incremental exercise tests, either of them could be used.     

Modelling Aggregation on the Large Scale and Regularity on the Small Scale in Spatial Point Pattern Datasets

We consider a dependent thinning of a regular point process with the aim of obtaining aggregation on the large scale and regularity on the small scale in the resulting target point process of retained points. Various parametric models for the underlying processes are suggested and the properties of the target point process are studied. Simulation and inference procedures are discussed when a realization of the target point process is observed, depending on whether the thinned points are observed or not. The paper extends previous work by Dietrich Stoyan on interrupted point processes.     

Response of wild bee communities to beekeeping,urbanization, and flower availability

Urban Ecosystems - Wild bees provide pollination services and are currently declining at the global scale. A potential cause for this decline is competitive interactions with domestic honey bees....     

Anisotropy of Hölder Gaussian random fields: characterization,estimation, and application to image textures

The characterization and estimation of the Hölder regularity of random fields has long been an important topic of Probability theory and Statistics. This notion of regularity has also been widely used in image analysis to measure the roughness of textures. However, such a measure is rarely sufficient to characterize textures as it does not account for their directional properties (e.g., isotropy and anisotropy). In this paper, we present an approach to further characterize directional properties associated with the Hölder regularity of random fields. Using the spectral density, we define a notion of asymptotic topothesy which quantifies directional contributions of field high-frequencies to the Hölder regularity. This notion is related to the topothesy function of the so-called anisotropic fractional Brownian fields, but is defined in a more generic framework of intrinsic random fields. We then propose a method based on multi-oriented quadratic variations to estimate this asymptotic topothesy. Eventually, we evaluate this method on synthetic data and apply it for the characterization of historical photographic papers.     

Governance and performance of MFIs: the Cameroon case

The main challenge of microfinance institutions and social economy firms remains their survival, and to meet this challenge, MFIs need to be competitive. The poor performance of MFIs is usually attributed to their decision-making and operational processes. The governance of MFIs is therefore identified as one of their main risks. Despite this, governance is still little explored in these organizations and empirical studies find a weak relationship between classical governance mechanisms and MFI performance, especially for the MFIs situated in Africa (Thrikawala et al. in Asian J Financ Account 5(1):160–182, 2013a). In this study, we examine whether the effect of governance mechanisms on the performance of MFIs differs according to their legal status in the Cameroonian context. On the one hand, our empirical results show that there is a significant relationship between some specific governance mechanisms and MFIs’ performance. On the other hand, adjusting the governance mechanisms according to the MFIs’ legal status improves their efficiency. The analysis of the impact of the governance mechanisms on the performance of MFIs requires not only an approach that is specific to this sector but also an approach that is adapted to their legal status. Moreover, from a managerial point of view, it would be desirable to adjust the governance mechanisms, depending on the legal status of the MFIs, to make them more efficient from the social as well as the financial standpoint.     

Influence and sensitivity measures in correspondence analysis

Since correspondence analysis appears to be sensitive to outliers, it is important to be able to evaluate the sensitivity of the data on the results. This article deals with measuring the influence of rows and columns on the results obtained with correspondence analysis. To establish the influence of individuals on the analysis, we use the notion of influence curve and we propose a general criterion based on the mean square error to measure the sensitivity of the correspondence analysis and its robustness. A numerical example is presented to illustrate the notions developed in this article.     

Various Approaches for Predicting Land Cover in Mountain Areas

Using former maps, geographers intend to study the evolution of the land cover in order to have a prospective approach on the future landscape; predictions of the future land cover, by the use of older maps and environmental variables, are usually done through the GIS (Geographic Information System). We propose here to confront this classical geographical approach with statistical approaches: a linear parametric model (polychotomous regression modeling) and a nonparametric one (multilayer perceptron). These methodologies have been tested on two real areas on which the land cover is known at various dates; this allows us to emphasize the benefit of these two statistical approaches compared to GIS and to discuss the way GIS could be improved by the use of statistical models.