23 research outputs found
Three essays on social interactions and education : theory and application
Lâobjectif principal de cette thĂšse est de proposer des mĂ©thodes dâidentification des effets qui dĂ©coulent des interactions sociales dans le contexte Ă©ducatif. La pertinence de ma recherche se trouve Ă trois niveaux : 1) elle nous aide Ă mieux mesurer lâimpact du rĂ©seau social sur les comportements individuels ; 2) elle amĂ©liore notre comprĂ©hension de phĂ©nomĂšnes sociaux nĂ©gatifs tels que lâobĂ©sitĂ© ou le dĂ©crochage scolaire ; 3) elle permet de proposer des politiques publiques adaptĂ©es, qui permettent dâexploiter au mieux les effets qui dĂ©coulent de ces interactions sociales en milieu scolaire. Lâatteinte de nos objectifs se fait Ă travers trois chapitres. Le premier chapitre propose une nouvelle stratĂ©gie dâestimation de lâinfluence du rĂ©seau social sur les dĂ©cisions individuelles dans un contexte dâinteractions en rĂ©seau Ă lâaide dâexpĂ©riences randomisĂ©es. Le chapitre combine le modĂšle structurel dâinteractions sociale dĂ©veloppĂ© par BramoullĂ© et al. [2009] avec une expĂ©rience randomisĂ©e. Des conditions dâidentification sont fournies et le modĂšle est estimĂ© et validĂ© sur des donnĂ©es expĂ©rimentales recueillies pour lâĂ©valuation dâun programme de bourses dâĂ©tudes en Colombie. De par sa conception, la randomisation est au niveau de lâĂ©lĂšve. Les donnĂ©es sur rĂ©seaux dâamitiĂ© rĂ©vĂšlent que les Ă©tudiants traitĂ©s et non traitĂ©s interagissent ensemble. En plus de fournir des preuves sur la prĂ©sence dâeffets de pairs dans la frĂ©quentation scolaire, le chapitre conclut que la non prise en considĂ©ration des interactions sociales de pairs conduit Ă une surestimation de lâimpact rĂ©el du programme. Lâobjectif du deuxiĂšme chapitre est de proposer un modĂšle qui tient compte de lâhĂ©tĂ©rogĂ©nĂ©itĂ© des effets de pairs entre les diffĂ©rentes catĂ©gories dâindividus dans un cadre dâinteractions en rĂ©seau. Les catĂ©gories peuvent se composer du genre ou de la race de lâindividu, entre autres. Des conditions dâidentification dâun modĂšle qui gĂ©nĂ©ralise celui proposĂ© par BramoullĂ© et al. [2009] sont dĂ©rivĂ©es, et lâhĂ©tĂ©rogĂ©nĂ©itĂ© des effets de pairs est permise Ă lâintĂ©rieur et entre les catĂ©gories. Ă lâaide des donnĂ©es Add Health, le chapitre explore lâhĂ©tĂ©rogĂ©nĂ©itĂ© sur le poids des adolescents mesurĂ© par leur indice de masse corporelle, utilisant Ă la fois le genre et une catĂ©gorisation basĂ©e sur leur groupe racial. Les rĂ©sultats montrent que lâeffet positif endogĂšne trouvĂ© en utilisant le modĂšle homogĂšne prĂ©sente de lâhĂ©tĂ©rogĂ©nĂ©itĂ© lorsque lâon considĂšre ces deux catĂ©gorisations. Alors que les deux premiers chapitres de cette thĂšse Ă©tudient les rĂ©seaux dâamitiĂ© dans une tentative dâidentifier les effets qui rĂ©sultent des interactions sociales, le troisiĂšme chapitre considĂšre le rĂ©seau de partage de cours -course-overlap- fourni par les Ă©tudes Add Health et AHAA. Le modĂšle est agrĂ©gĂ© au niveau local et a la particularitĂ©, contrairement Ă dâautres Ă©tudes sur les effets de pairs, que la matrice dâinteractions sociales considĂšre les marges extensive et intensive. De plus, les interactions de ce type sont meilleures dans la conception des politiques scolaires. Lâestimation du modĂšle sur les rĂ©sultats scolaires gĂ©nĂ©raux, en mathĂ©matiques et en sciences rĂ©vĂšle la prĂ©sence dâeffets dâinteraction sociales positives et significatives en utilisant les techniques des moindres carrĂ©s Ă deux Ă©tapes et la mĂ©thode des moments gĂ©nĂ©ralisĂ©s.The aim of this thesis is to investigate identification of peer effects and their application on a large set of outcomes, going from school attendance to obesity. The relevance of this research relies on three main points: 1) it allows better measurrement of effects stemming from social interactions, thus providing some answer to the numerous econometric issues that make the study of peer effects a lot challenging; 2) it improves our comprehension of negative social phenomena, including the incidence of school dropouts and obesity; 3) it proposes better public policies aiming at fighting against such phenomena by exploiting social network effects that contribute to amplify them. The different objectives of this thesis are investigated in three different chapters. The first chapter proposes a new strategy for estimating the influence of the social network on individual decisions in a network context using randomized experiments. It combinates the structural social network model developed by BramoullĂ© et al. [2009] and randomized experiments. New identification conditions that mostly require balance in the characteristics of friends between treatment and control groups are provided. The model is estimated and validated on experimental data collected for the evaluation of a scholarship program in Colombia. By design, randomization is at the student-level. Friendship data reveals that treated and untreated students interact together. Besides providing evidence of peer effects in schooling, the chapter concludes that ignoring peer effects would have led to an overestimation of the program actual impact. The aim of the second chapter is to propose a model that accounts for heterogeneity in peer effects between individual categories in a network setting. Identification conditions of a network-based interactions model that generalizes the one proposed by BramoullĂ© et al. [2009] are derived, and heterogeneity of peer effects is allowed within and between categories of individuals. Using the Add-Health dataset, the study explores heterogeneity in adolescents weight using both gender and racial categorizations. The results show that the positive endogenous effect found using the homogeneous model is actually heterogeneous when considering both gender and racial categorizations, as for example, females seem to be more influenced by their female friends than by their male friends. While the first two chapters consider friendship networks in an attempt to identify the effects that result from social interactions, the third chapter considers the course-overlaps network. The model is local agregate and has the feature, unlike other studies of peer effects, that the interaction matrix accounts for the extensive and intensive margins. Interactions of this type are better to design school policies. The chapter then proceeds to estimation of peer effects in overall GPA and GPAs in both mathematics and science courses using the Add Heakth and AHAA datasets. The results reveal the presence of positive and significant social interaction effects using both 2SLS and GMM estimation techniques
Accounting for Peer Effects in Treatment Response
When one's treatment status affects the outcomes of others, experimental data are not sufficient to identify a treatment causal impact. In order to account for peer effects in program response, we use a social network model. We estimate and validate the model on experimental data collected for the evaluation of a scholarship program in Colombia. By design, randomization is at the student-level. Friendship data reveals that treated and untreated students interact together. Besides providing evidence of peer effects in schooling, we find that ignoring peer effects would have led us to overstate the program actual impact
Genetic contribution of breast cancer genes in women of black African origin
Breast cancer (BC) is an increasing public health issue worldwide. BC incidence and mortality rates are rising in transitioning countries in Africa, with the most rapid increase occurring in Sub-Saharan Africa (SSA). Female BC represents 25.8% of all cancer diagnosis in SSA. Early age at onset, high grade and triple negative tumors are hallmarks of BC in this region, associated with germline pathogenic variants in susceptibility genes. While several genes have been associated with genetic predisposition (BRCA1, BRCA2, PALB2, TP53, PTEN, CDH1, STK11, ATM, CHEK2, NBN, BARD1, BRIP1, RAD50, RAD51C, RAD51D, ⊠), most studies have reported contribution of BRCA1 and BRCA2 pathogenic variants. Genetic contribution of BRCA genes has been estimated at 27% in Caucasian women. Available data from population of African origin are scarce and have mainly focused on pathogenic variants of BRCA1 and BRCA2. Reports from main studies on large sample size highlighted that BRCA1 still the major gene associated with BC in SSA. In addition, BRCA2, PALB2, and P53, are also on the top major genes with high penetrance, associated with BC. Mutation spectrum of BC genes in black African women seems to be different from Caucasian with increasing number of founder mutations identified. We hypothesis that the genetic contribution of known BC genes may be different between women of black African origin compared to Caucasians. In this review we explore the genetic contribution of known breast cancer genes in women of African origin, and discuss perspectives for prevention and patients care strategies in the era of precision medicine
Gene expression profiling in blood from cerebral malaria patients and mild malaria patients living in Senegal
International audienceBACKGROUND:Plasmodium falciparum malaria remains a major health problem in Africa. The mechanisms of pathogenesis are not fully understood. Transcriptomic studies may provide new insights into molecular pathways involved in the severe form of the disease.METHODS:Blood transcriptional levels were assessed in patients with cerebral malaria, non-cerebral malaria, or mild malaria by using microarray technology to look for gene expression profiles associated with clinical status. Multi-way ANOVA was used to extract differentially expressed genes. Network and pathways analyses were used to detect enrichment for biological pathways.RESULTS:We identified a set of 443 genes that were differentially expressed in the three patient groups after applying a false discovery rate of 10%. Since the cerebral patients displayed a particular transcriptional pattern, we focused our analysis on the differences between cerebral malaria patients and mild malaria patients. We further found 842 differentially expressed genes after applying a false discovery rate of 10%. Unsupervised hierarchical clustering of cerebral malaria-informative genes led to clustering of the cerebral malaria patients. The support vector machine method allowed us to correctly classify five out of six cerebral malaria patients and six of six mild malaria patients. Furthermore, the products of the differentially expressed genes were mapped onto a human protein-protein network. This led to the identification of the proteins with the highest number of interactions, including GSK3B, RELA, and APP. The enrichment analysis of the gene functional annotation indicates that genes involved in immune signalling pathways play a role in the occurrence of cerebral malaria. These include BCR-, TCR-, TLR-, cytokine-, FcΔRI-, and FCGR- signalling pathways and natural killer cell cytotoxicity pathways, which are involved in the activation of immune cells. In addition, our results revealed an enrichment of genes involved in Alzheimer's disease.CONCLUSIONS:In the present study, we examine a set of genes whose expression differed in cerebral malaria patients and mild malaria patients. Moreover, our results provide new insights into the potential effect of the dysregulation of gene expression in immune pathways. Host genetic variation may partly explain such alteration of gene expression. Further studies are required to investigate this in African populations
Ătude in vitro de lâeffet antifalcĂ©miant des globules rouges et de lâactivitĂ© antioxydante dâextraits de la poudre de racines de Maytenus senegalensis Lam (Celestraceae)
La drĂ©panocytose est une hĂ©moglobinopathie largement rĂ©pandue chez les populations africaines noires. Actuellement, trĂšs peu de traitements conventionnels existent sur le marchĂ©, dâoĂč le recours Ă la mĂ©decine traditionnelle. Maytenus senegalensis est une plante prescrite par les tradipraticiens dans la prise en charge de la drĂ©panocytose. LâactivitĂ© antifalcĂ©miante des extraits de la poudre de racines de Maytenus senegalensis a Ă©tĂ© Ă©tudiĂ©e dans ce travail. AprĂšs obtention de lâextrait hexanique par extraction Ă lâaide dâun Soxhlet, le marc est macĂ©rĂ© dans de lâacĂ©tate dâĂ©thyle puis dans du mĂ©thanol pour donner les extraits correspondants. LâactivitĂ© des fractions a Ă©tĂ© Ă©valuĂ©e sur des drĂ©panocytes de type SS. Les activitĂ©s antifalcĂ©miantes les plus importantes ont Ă©tĂ© observĂ©es pour les fractions polaires du mĂ©thanol et de lâacĂ©tate dâĂ©thyle avec des taux dâinversion de la falciformation respectivement de 77% et de 65% Ă 10 mg/mL. Les activitĂ©s antioxydantes de M. senegalensis (CI50 = 0,195 ± 0,004 mg/mL) et de lâacide ascorbique (CI50 = 0,078 ± 0,002 mg/mL) ont Ă©tĂ© dĂ©terminĂ©es. Les pouvoirs antioxydants (PA) montrent que lâactivitĂ© antiradicalaire de lâacide ascorbique (PA = 12,85) est 2,5 fois meilleure que celle de M. senegalensis (PA = 5,14). Les rĂ©sultats de lâĂ©tude justifient lâutilisation traditionnelle des racines de Maytenus senegalensis dans la prise en charge de la drĂ©panocytose.Mots clĂ©s : HĂ©moglobine, drĂ©panocytose, Maytenus senegalensis, activitĂ© antifalcĂ©miante, stress oxydant, radicaux libres, activitĂ© antioxydante
NCR3 polymorphism, haematological parameters, and severe malaria in Senegalese patients
Background Host factors, including host genetic variation, have been shown to influence the outcome of Plasmodium falciparum infection. Genome-wide linkage studies have mapped mild malaria resistance genes on chromosome 6p21, whereas NCR3-412 polymorphism (rs2736191) lying within this region was found to be associated with mild malaria. Methods Blood samples were taken from 188 Plasmodium falciparum malaria patients (76 mild malaria patients, 85 cerebral malaria patients, and 27 severe non-cerebral malaria patients). NCR3-412 (rs2736191) was analysed by sequencing, and haematological parameters were measured. Finally, their association with clinical phenotypes was assessed. Results We evidenced an association of thrombocytopenia with both cerebral malaria and severe non-cerebral malaria, and of an association of high leukocyte count with cerebral malaria. Additionally, we found no association of NCR3-412 with either cerebral malaria, severe non-cerebral malaria, or severe malaria after grouping cerebral malaria and severe non-cerebral malaria patients. Conclusions Our results suggest that NCR3 genetic variation has no effect, or only a small effect on the occurrence of severe malaria, although it has been strongly associated with mild malaria. We discuss the biological meaning of these results. Besides, we confirmed the association of thrombocytopenia and high leukocyte count with severe malaria phenotypes
Genetic Determination and Linkage Mapping of Plasmodium falciparum Malaria Related Traits in Senegal
Plasmodium falciparum malaria episodes may vary considerably in their severity and clinical manifestations. There is good evidence that host genetic factors contribute to this variability. To date, most genetic studies aiming at the identification of these genes have used a case/control study design for severe malaria, exploring specific candidate genes. Here, we performed a family-based genetic study of falciparum malaria related phenotypes in two independent longitudinal survey cohorts, as a first step towards the identification of genes and mechanisms involved in the outcome of infection. We studied two Senegalese villages, Dielmo and Ndiop that differ in ethnicity, malaria transmission and endemicity. We performed genome-scan linkage analysis of several malaria-related phenotypes both during clinical attacks and asymptomatic infection. We show evidence for a strong genetic contribution to both the number of clinical falciparum malaria attacks and the asymptomatic parasite density. The asymptomatic parasite density showed linkage to chromosome 5q31 (LODâ=â2.26, empirical pâ=â0.0014, Dielmo), confirming previous findings in other studies. Suggestive linkage values were also obtained at three additional chromosome regions: the number of clinical malaria attacks on chromosome 5p15 (LODâ=â2.57, empirical pâ=â0.001, Dielmo) and 13q13 (LODâ=â2.37, empirical pâ=â0.0014 Dielmo), and the maximum parasite density during asymptomatic infection on chromosome 12q21 (LODâ=â3.1, empirical p<10â4, Ndiop). While regions of linkage show little overlap with genes known to be involved in severe malaria, the four regions appear to overlap with regions linked to asthma or atopy related traits, suggesting that common immune related pathways may be involved
Susbsidies and cluster policy in French NUTS3 Regions. Direct and indirect effects through space and co-patenting networks
International audienc
Financial market reaction to cyberattacks
International audienceDrawing upon an extensive dataset comprising 3,680 cyberattacks on firms listed in 5 stock markets, our main objective is to ascertain the financial market reaction based on a hybrid valuation inspired by the event study methodology and a counterfactual analysis. Analyses concern three dates that are specific to cyberattacks: 1) the accident date; 2) the first notice date; and 3) the original loss start date. Results indicate that there is a negative abnormal return for the NASDAQ after the accident date. The reactions of the NASDAQ and NYSE are similar, and negative for the first notice date but positive after the original loss start date. In the European context, cumulative abnormal returns are negative for French and German companies after the first notice date