6 research outputs found
Ego-centred models of social networks: the social atom
Mención Internacional en el título de doctorThis thesis set out to contribute to the realm of social physics, with a particular
focus on human social networks. Our approach, however, is somewhat
di
erent from what is typical in disciplines such as complex systems or statistical
physics. Rather than simplifying the features of the constituents of
our system (people), and stressing their rules of interaction, we focus on
better understanding those very same constituents, modelling them as social
atoms. Our rationale is that a better understanding of such an atom
may shed light on how (and why) it interacts with other atoms to form
social collectives.
Given its robustness and the evolutionary roots of its premises, we use
the Social Brain Hypothesis as our departure point. This theory states that
the evolutionary drive behind the development of large brains in humans
was the need to process social information and that the limited capacity of
our brains imposes a limit to the number of relationships we can manage—
the so-called “Dunbar’s number”, roughly 150. Moreover, evidence keeps
revealing that these relationships are further organised in a series of hierarchically
inclusive layers with decreasing emotional intensity, whose sizes
exhibit a more or less constant scaling. Notwithstanding the empirical evidence,
neither the presence of scaling in the organisation of personal networks
nor its connection with limited cognitive skills had been explained
so far.
In Chapter 2 we present a mathematical model that solves this puzzle.
The assumptions of the model are quite simple, and well founded on empirical
evidence. Firstly, the number of relationships we maintain tends
to be stable on average. Secondly, these relationships are costly, and our resources are limited. With these two premises, our results show that the
hierarchical organisation emerges naturally from the principle of maximum
entropy. Not only that, but we also predict a hitherto unnoticed regime of
organisation whose existence we prove using several datasets from communities
of immigrants.
The former model considers that relationships can only belong to a
discrete set of categories (layers). In Chapter 3 we extend it so that relationships
are classified in a continuum. This modification allows us to test
the model with data from very di
erent sources such as online communications,
face-to-face contacts, and phone calls. Our results show that the two
regimes of organisation found in the previous model persist in this variant,
and reveal the underlying existence of a (universal) scaling parameter
which does not depend on any particular number of layers.
To incorporate these ideas into socio-centric models, we build on the
so-called Structural Balance Theory. This theory, underpinned by psychological
motivations, posits that the structure of social networks of positive
and negative relationships are highly interdependent. However, the theory
has received little empirical validation, and negative social relationships
are poorly understood—both from an ego-centric and a socio-centric perspective.
For that reason, we turn to developing an experimental software
in order to gather data within a school.
In Chapters 4 and 5 we present results from these experiments. In
Chapter 4 we analyse the socio-centric networks using machine learning
techniques and find that the structure of positive and negative networks
is indeed very much connected. Besides, we study the two types of networks
separately, showing that they exhibit quite distinct features and that
gender e
ects in negative social networks are weak and asymmetrical for
boys and girls. In Chapter 5, on the other hand, we focus on the structure
of negative personal networks. Remarkably, using data from two di
erent
experimental settings, we show that the structure of personal networks
of negative relationships mirrors that of the positive ones and exhibits a
similar scaling—albeit their size is significantly smaller.
Chapter 6 summarises our results and presents future (and current) lines
of investigation. Among them, we outline a model of a social fluid that
uses the insights gained with this thesis to build a model of social collectives
as ensembles of personal networks. This model is compatible, at the micro-level, with the observations of the social brain hypothesis, and, at
the macro-level, with the premises of the structural balance theory.This thesis would not have been possible without the support of Fundación
BBVA through its 2016 call project ”Los números de Dunbar y la estructura
de las sociedades digitales: modelización y simulación (DUNDIG)”,
and we are very thankful for it. Support for early stages of this work
through projects IBSEN (European Commission, H2020 FET Open RIA
662725) and VARIANCE (Ministerio de Economía y Competitividad/FEDER,
project no. FIS2015-64349-P) is also acknowledgedPrograma Oficial de Doctorado en Ingeniería Matemática por la Universidad Carlos III de MadridPresidente: Javier Martín Buldú.- Secretario: José Luis Molina González.- Vocal: Roberta Sinatr
Risk Factors for COVID-19 in Inflammatory Bowel Disease: A National, ENEIDA-Based Case–Control Study (COVID-19-EII)
(1) Scant information is available concerning the characteristics that may favour the acquisition of COVID-19 in patients with inflammatory bowel disease (IBD). Therefore, the aim of this study was to assess these differences between infected and noninfected patients with IBD. (2) This nationwide case-control study evaluated patients with inflammatory bowel disease with COVID-19 (cases) and without COVID-19 (controls) during the period March-July 2020 included in the ENEIDA of GETECCU. (3) A total of 496 cases and 964 controls from 73 Spanish centres were included. No differences were found in the basal characteristics between cases and controls. Cases had higher comorbidity Charlson scores (24% vs. 19%; p = 0.02) and occupational risk (28% vs. 10.5%; p < 0.0001) more frequently than did controls. Lockdown was the only protective measure against COVID-19 (50% vs. 70%; p < 0.0001). No differences were found in the use of systemic steroids, immunosuppressants or biologics between cases and controls. Cases were more often treated with 5-aminosalicylates (42% vs. 34%; p = 0.003). Having a moderate Charlson score (OR: 2.7; 95%CI: 1.3-5.9), occupational risk (OR: 2.9; 95%CI: 1.8-4.4) and the use of 5-aminosalicylates (OR: 1.7; 95%CI: 1.2-2.5) were factors for COVID-19. The strict lockdown was the only protective factor (OR: 0.1; 95%CI: 0.09-0.2). (4) Comorbidities and occupational exposure are the most relevant factors for COVID-19 in patients with IBD. The risk of COVID-19 seems not to be increased by immunosuppressants or biologics, with a potential effect of 5-aminosalicylates, which should be investigated further and interpreted with caution
Beyond Dunbar circles: a continuous description of social relationships and resource allocation
We discuss the structure of human relationship patterns in terms of a new formalism that allows to study resource allocation problems where the cost of the resource may take continuous values. This is in contrast with the main focus of previous studies where relationships were classified in a few, discrete layers (known as Dunbar’s circles) with the cost being the same within each layer. We show that with our continuum approach we can identify a parameter η
that is the equivalent of the ratio of relationships between adjacent circles in the discrete case, with a value η∼6
. We confirm this prediction using three different datasets coming from phone records, face-to-face contacts, and interactions in Facebook. As the sample size increases, the distributions of estimated parameters smooth around the predicted value of η
. The existence of a characteristic value of the parameter at the population level indicates that the model is capturing a seemingly universal feature on how humans manage relationships. Our analyses also confirm earlier results showing the existence of social signatures arising from having to allocate finite resources into different relationships, and that the structure of online personal networks mirrors those in the off-line world.We are very thankful to Prof. Ben Zhao for granting us access to his Facebook dataset, and to Dr. Valerio Arnaboldi for sharing with us the final, curated dataset just as they used it in their paper. This research has been funded by project BASIC (PGC2018-098186-B-I00) funded by MCIN/AEI/ 10.13039/501100011033 and by ERDF A way of making Europe
Structural measures of personal networks predict migrants' cultural backgrounds: an explanation from Grid/Group theory
Culture and social structure are not separated analytical domains but intertwined phenomena observable in personal networks. Drawing on a personal networks dataset of migrants in the United States and Spain, we show that the country of origin, a proxy for diverse languages and cultural institutions, and religion may be predicted by specific combinations of personal network structural measures (closeness, clustering, betweenness, average degree, etc). We obtain similar results applying three different methods (a multinomial logistic regression, a Random Forest algorithm, and an artificial neural network). This finding is explained within the framework of the Grid/Group theory that has long posed the interdependence of social structural and cultural features of human groups.This research has been funded by the National Science Foundation (BCS-0417429), the MINECO-FEDER (PGC2018-098186-B-I00, J.O., A.S.), the Comunidad de Madrid (PRACTICO-CM), and the UC3M (CAVTIONS-CM-UC3M)
Nationwide COVID-19-EII Study : Incidence, Environmental Risk Factors and Long-Term Follow-Up of Patients with Inflammatory Bowel Disease and COVID-19 of the ENEIDA Registry
We aim to describe the incidence and source of contagion of COVID-19 in patients with IBD, as well as the risk factors for a severe course and long-term sequelae. This is a prospective observational study of IBD and COVID-19 included in the ENEIDA registry (53,682 from 73 centres) between March-July 2020 followed-up for 12 months. Results were compared with data of the general population (National Centre of Epidemiology and Catalonia). A total of 482 patients with COVID-19 were identified. Twenty-eight percent were infected in the work environment, and 48% were infected by intrafamilial transmission, despite having good adherence to lockdown. Thirty-five percent required hospitalization, 7.9% had severe COVID-19 and 3.7% died. Similar data were reported in the general population (hospitalisation 19.5%, ICU 2.1% and mortality 4.6%). Factors related to death and severe COVID-19 were being aged ≥ 60 years (OR 7.1, 95% CI: 1.8-27 and 4.5, 95% CI: 1.3-15.9), while having ≥2 comorbidities increased mortality (OR 3.9, 95% CI: 1.3-11.6). None of the drugs for IBD were related to severe COVID-19. Immunosuppression was definitively stopped in 1% of patients at 12 months. The prognosis of COVID-19 in IBD, even in immunosuppressed patients, is similar to that in the general population. Thus, there is no need for more strict protection measures in IBD
Risk Factors for COVID-19 in Inflammatory Bowel Disease: A National, ENEIDA-Based Case–Control Study (COVID-19-EII)
(1) Scant information is available concerning the characteristics that may favour the acquisition of COVID-19 in patients with inflammatory bowel disease (IBD). Therefore, the aim of this study was to assess these differences between infected and noninfected patients with IBD. (2) This nationwide case–control study evaluated patients with inflammatory bowel disease with COVID-19 (cases) and without COVID-19 (controls) during the period March–July 2020 included in the ENEIDA of GETECCU. (3) A total of 496 cases and 964 controls from 73 Spanish centres were included. No differences were found in the basal characteristics between cases and controls. Cases had higher comorbidity Charlson scores (24% vs. 19%; p = 0.02) and occupational risk (28% vs. 10.5%; p < 0.0001) more frequently than did controls. Lockdown was the only protective measure against COVID-19 (50% vs. 70%; p < 0.0001). No differences were found in the use of systemic steroids, immunosuppressants or biologics between cases and controls. Cases were more often treated with 5-aminosalicylates (42% vs. 34%; p = 0.003). Having a moderate Charlson score (OR: 2.7; 95%CI: 1.3–5.9), occupational risk (OR: 2.9; 95%CI: 1.8–4.4) and the use of 5-aminosalicylates (OR: 1.7; 95%CI: 1.2–2.5) were factors for COVID-19. The strict lockdown was the only protective factor (OR: 0.1; 95%CI: 0.09–0.2). (4) Comorbidities and occupational exposure are the most relevant factors for COVID-19 in patients with IBD. The risk of COVID-19 seems not to be increased by immunosuppressants or biologics, with a potential effect of 5-aminosalicylates, which should be investigated further and interpreted with caution