1,721,296 research outputs found
Sample selection bias in credit scoring models
No full textOne of the aims of credit scoring models is to predict the probability of repayment of any applicant and yet such models are usually parameterised using a sample of accepted applicants only. This may lead to biased estimates of the parameters. In this paper we examine two issues. First, we compare the classification accuracy of a model based only on accepted applicants, relative to one based on a sample of all applicants. We find only a minimal difference, given the cutoff scores for the old model used by the data supplier. Using a simulated model we examine the predictive performance of models estimated from bands of applicants, ranked by predicted creditworthiness. We find that the lower the risk band of the training sample, the less accurate the predictions for all applicants. We also find that the lower the risk band of the training sample, the greater the overestimate of the true performance of the model, when tested on a sample of applicants within the same risk band ¾ as a financial institution would do. The overestimation may be very large. Second, we examine the predictive accuracy of a bivariate probit model with selection (BVP). This parameterises the accept-reject model allowing for (unknown) omitted variables to be correlated with those of the original good-bad model. The BVP model may improve accuracy if the loan officer has overridden a scoring rule. We find that a small improvement when using the BVP model is sometimes possible
Scoring by usage
No full textThis paper aims to discover whether the predictive accuracy of a new applicant scoring model for a credit card can be improved by estimating separate scoring models for applicants who are predicted to have high or low usage of the card. Two models are estimated. First we estimate a model to explain the desired usage of a card, and second we estimate separately two further scoring models, one for those applicants whose usage is predicted to be high, and one for those for whom it is predicted to be low. The desired usage model is a two-stage Heckman model to take into account the fact that the observed usage of accepted applicants is constrained by their credit limit. Thus a model of the determinants of the credit limit, and one of usage, are both estimated using Heckman's ML estimator. We find a large number of variables to be correlated with desired usage. We also find that the two stage scoring methodology gives only very marginal improvements over a single stage scoring model, that we are able to predict a greater percentage of bad payers for low users than for high users and a greater percentage of good payers for high users than for low users
Michael, R. P. et Crook, J. H. (Ed.). — Comparative Ecology and Behaviour of Primates. Academic Press, London and New York, 1973
No full textBourlière François. Michael, R. P. et Crook, J. H. (Ed.). — Comparative Ecology and Behaviour of Primates. Academic Press, London and New York, 1973. In: La Terre et La Vie, Revue d'Histoire naturelle, tome 28, n°1, 1974. p. 163
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Velocity invariance of preferred axis of motion for single spot stimuli in simple cells of cat striate cortex
No full textDirectional tuning for motion of a long bar and a spot was compared quantitatively over a wide range of velocities in 23 simple cells of cat striate cortex whose “on” and “off” receptive field subregions had been mapped with optimally oriented, stationary flash-presented bars. Tuning curves were derived using stimuli whose polarity of contrast was appropriate for the dominant receptive field subregion of each cell (i.e. light stimuli for on-subregions and dark stimuli for off-subregions); stimulus sweep was centred accurately on the centre of that subregion. Bar stimuli were of optimal width, and spot diameter was equal to the width of the bars. In all simple cells, preferred axis of motion for a long bar was invariant with velocity, being orthogonal to preferred orientation, as assessed with a stationary flash-presented bar. In 20 of 23 simple cells, preferred axis for spot motion was approximately orthogonal to that for bar motion (i.e., parallel to preferred orientation) at all velocities tested, including those just above threshold for spot stimuli. However, tuning for the spot became sharper as velocity was increased, due to an increase in response to the spot moving along the preferred axis and a decrease in response to spot motion along other axes, including the preferred axis for the bar. Both preferred and upper cut-off velocity were consistently higher for spot than for bar motion. The remaining 3 simple cells showed no response to spot motion at any velocity, and their preferred axis of motion for the shortest bar which evoked a consistent response was the same as that for a long bar. We conclude that simple cells respond to motion of a spot per se and not just to its oriented components, and that in most simple cells preferred axis for spot motion is genuinely approximately orthogonal to that for motion of a long bar. A spatio-temporal filter model incorporating intracortical feedforward facilitation along the long axis of the receptive field can account for the observed differences in axis preference and velocity sensitivity for spot and bar motion
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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