1,720,967 research outputs found
Tsallis entropy for cross-shareholding network configurations
Get PDFIn this work, we develop the Tsallis entropy approach for examining the 1
cross-shareholding network of companies traded on the Italian stock market. In such a network, 2
the nodes represent the companies, and the links represent the ownership. Within this context, we 3
introduce the out-degree of the nodes – which represents the diversification – and the in-degree 4
of them – capturing the integration. Diversification and integration allow a clear description 5
of the industrial structure formed by the considered companies. The stochastic dependence of 6
diversification and integration is modelled through copulas. We argue that copulas are well suited 7
for modelling the joint distribution. The analysis of the stochastic dependence between integration 8
and diversification by means of the Tsallis entropy gives a crucial information on the reaction of 9
the market structure to the external shocks, - on the basis of some relevant cases of dependence 10
between the considered variables. Indeed, the considered entropy framework provides insights on 11
the relationship between in-degree and out-degree dependence structure and market polarisation or 12
fairness. Moreover, the interpretation of the results in the light of the Tsallis entropy parameter gives 13
relevant suggestions for policymakers who aim at shaping the industrial context for having high 14
polarisation or fair joint distribution of diversification and integration. Furthermore, a discussion 15
of possible parametrisations of the in-degree and out-degree marginal distribution, – by means of 16
power laws or exponential functions, – is also carried out. An empirical experiment on a large 17
dataset of Italian companies validates the theoretical framework
Investigating the Configurations in Cross-Shareholding: A Joint Copula-Entropy Approach
Get PDFThe complex nature of the interlacement of economic actors is quite evident at the level of the Stock market, where any company may actually interact with the other companies buying and selling their shares. In this respect, the companies populating a Stock market, along with their connections, can be effectively modeled through a directed network, where the nodes represent the companies, and the links indicate the ownership. This paper deals with this theme and discusses the concentration of a market. A cross-shareholding matrix is considered, along with two key factors: the node out-degree distribution which represents the diversification of investments in terms of the number of involved companies, and the node in-degree distribution which reports the integration of a company due to the sales of its own shares to other companies. While diversification is widely explored in the literature, integration is most present in literature on contagions. This paper captures such quantities of interest in the two frameworks and studies the stochastic dependence of diversification and integration through a copula approach. We adopt entropies as measures for assessing the concentration in the market. The main question is to assess the dependence structure leading to a better description of the data or to market polarization (minimal entropy) or market fairness (maximal entropy). In so doing, we derive information on the way in which the in- and out-degrees should be connected in order to shape the market. The question is of interest to regulators bodies, as witnessed by specific alert threshold published on the US mergers guidelines for limiting the possibility of acquisitions and the prevalence of a single company on the market. Indeed, all countries and the EU have also rules or guidelines in order to limit concentrations, in a country or across borders, respectively. The calibration of copulas and model parameters on the basis of real data serves as an illustrative application of the theoretical proposal
Effect of religious rules on time of conception in Romania from 1905 to 2001
No full textSTUDY QUESTION:
Does the interdiction of sexual intercourse during Nativity and Lent fasting periods have any effect on when babies are conceived in Romania, in the 20th century?
SUMMARY ANSWER:
Based on date of birth records from the 20th century, Lent had a greater effect than the Nativity fast on conception within the Eastern Orthodox (ORTHD) population.
WHAT IS KNOWN ALREADY:
Seasonality of births (and therefore of conception) is affected by geographical factors (latitude, weather, day-length). Other demographic, economic and socio-cultural characteristics (education, ethnicity, religion) have been proved to have an influence on conception.
STUDY DESIGN, SIZE, DURATION:
The analyzed data consists of registered daily birth records for a long time series (35 429 points = 365 (days/year) × 97 years + 24 leap years), with 24 947 061 births in Romania over the period 1905-2001. The data were obtained from the 1992 and 2002 censuses.
PARTICIPANTS/MATERIALS, SETTING, METHODS:
Based on the reported birth date of each person, the estimated date of conception is computed using a standard gestation period of 280 days. The population was grouped into two categories (ORTHD and Non-Orthodox (NORTHD)) based on religious affiliation. Data analysis is performed in the same manner for both groups. Preliminary data analyses regarding seasonal variations in conception are considered first. Econometric models are applied and tested. The dependent variable in these models is the calculated date of conception, while the independent variables are: (i) religious affiliation; (ii) dates of Nativity and Lent fasts (the latter varies slightly from year to year); (iii) rural versus urban residence; (iv) length of day-light; (v) non-working days and (vi) trend. The models are tested for validity using analysis of variance while the regression coefficients are tested by the Student t-test.
MAIN RESULTS AND THE ROLE OF CHANCE:
All models are statistically valid (P < 0.01); all regression coefficients for the ORTHD group are valid (P < 0.01, except for rurality between 1990 and 2001, with P < 0.05). The data analysis indicates smaller standard error bars on the parameters for the ORTHD group as compared with the NORTHD group. The conclusion is that religious affiliation is an important factor in date of conception.
LIMITATIONS, REASONS FOR CAUTION:
The data do not refer to all births during the analyzed period, but only to those persons still alive at the 1992 and 2002 censuses. The date of conception was estimated assuming 280 days for gestation, which is a medically accepted time interval but will undoubtedly vary. However, the primary independent variables (Lent and Nativity fast at 48 and 40 days, respectively) are long enough to overlap the uncertainty in the conception date following the sexual intercourse event. We also must assume that the religious affiliation of the parents is well defined, based on the information given by their offspring at census time, and is the same for both parents.
WIDER IMPLICATIONS OF THE FINDINGS:
Our findings are consistent with other studies, which show differences between religious groups on date of conception, although we reach different conclusions regarding the influence of weather on fertility in Romania
Pitfalls in Testing with Linear Regression Model by OLS
No full textThis is a comment on “Ramadan fasting, sex-ratio at birth, and birth weight: No effects on Muslim
infants born in Germany” [Economic Letters, 2015] DOI
http://dx.doi.org/10.1016/j.econlet.2015.10.015. We show that due to some methodological
aspects the main conclusions of the above mentioned paper should be a little bit altered
Quantitative and Qualitative Analysis of Editor Behavior through Potentially Coercive Citations
Get PDFHow much is the h-index of an editor of a well-ranked journal improved due to citations which occur after his/her appointment? Scientific recognition within academia is widely measured nowadays by the number of citations or h-index. Our dataset is based on a sample of four editors from a well-ranked journal (impact factor, IF, greater than 2). The target group consists of two editors who seem to benefit by their position through an increased citation number (and subsequently h-index) within the journal. The total amount of citations for the target group is greater than 600. The control group is formed by another set of two editors from the same journal whose relations between their positions and their citation records remain neutral. The total amount of citations for the control group is more than 1200. The timespan for which the citations’ pattern has been studied is 1975–2015. Previous coercive citations for a journal’s benefit (an increase of its IF) has been indicated. To the best of our knowledge, this is a pioneering work on coercive citations for personal (editors’) benefit. Editorial teams should be aware about this type of potentially unethical behavior and act accordingly
A Theory of Best Choice Selection through Objective Arguments Grounded in Linear Response Theory Concepts
No full textIn this study, we propose how to use objective arguments grounded in statistical mechanics concepts in order to obtain a single number, obtained after aggregation, which would allow for the ranking of “agents”, “opinions”, etc., all defined in a very broad sense. We aim toward any process which should a priori demand or lead to some consensus in order to attain the presumably best choice among many possibilities. In order to specify the framework, we discuss previous attempts, recalling trivial means of scores—weighted or not—Condorcet paradox, TOPSIS (Technique for Order Preference by Similarity to Ideal Solution), etc. We demonstrate, through geometrical arguments on a toy example and with four criteria, that the pre-selected order of criteria in previous attempts makes a difference in the final result. However, it might be unjustified. Thus, we base our “best choice theory” on the linear response theory in statistical physics: we indicate that one should be calculating correlations functions between all possible choice evaluations, thereby avoiding an arbitrarily ordered set of criteria. We justify the point through an example with six possible criteria. Applications in many fields are suggested. Furthermore, two toy models, serving as practical examples and illustrative arguments are discussed
Investigating the Configurations in Cross-Shareholding: A Joint Copula-Entropy Approach
No full textThe complex nature of the interlacement of economic actors is quite evident at the level of the Stock market, where any company may actually interact with the other companies buying and selling their shares. In this respect, the companies populating a Stock market, along with their connections, can be effectively modeled through a directed network, where the nodes represent the companies, and the links indicate the ownership. This paper deals with this theme and discusses the concentration of a market. A cross-shareholding matrix is considered, along with two key factors: the node out-degree distribution which represents the diversification of investments in terms of the number of involved companies, and the node in-degree distribution which reports the integration of a company due to the sales of its own shares to other companies. While diversification is widely explored in the literature, integration is most present in literature on contagions. This paper captures such quantities of interest in the two frameworks and studies the stochastic dependence of diversification and integration through a copula approach. We adopt entropies as measures for assessing the concentration in the market. The main question is to assess the dependence structure leading to a better description of the data or to market polarization (minimal entropy) or market fairness (maximal entropy). In so doing, we derive information on the way in which the in- and out-degrees should be connected in order to shape the market. The question is of interest to regulators bodies, as witnessed by specific alert threshold published on the US mergers guidelines for limiting the possibility of acquisitions and the prevalence of a single company on the market. Indeed, all countries and the EU have also rules or guidelines in order to limit concentrations, in a country or across borders, respectively. The calibration of copulas and model parameters on the basis of real data serves as an illustrative application of the theoretical proposal
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
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