| 1. |
- Albert, J., et al.
(författare)
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Risk of HIV transmission from patients on antiretroviral therapy: A position statement from the Public Health Agency of Sweden and the Swedish Reference Group for Antiviral Therapy
- 2014
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Ingår i: Scandinavian Journal of Infectious Diseases. - : Informa UK Limited. - 0036-5548 .- 1651-1980. ; 46:10, s. 673-677
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Tidskriftsartikel (refereegranskat)abstract
- The modern medical treatment of HIV with antiretroviral therapy (ART) has drastically reduced the morbidity and mortality in patients infected with this virus. ART has also been shown to reduce the transmission risk from individual patients as well as the spread of the infection at the population level. This position statement from the Public Health Agency of Sweden and the Swedish Reference Group for Antiviral Therapy is based on a workshop organized in the fall of 2012. It summarizes the latest research and knowledge on the risk of HIV transmission from patients on ART, with a focus on the risk of sexual transmission. The risk of transmission via shared injection equipment among intravenous drug users is also examined, as is the risk of mother-to-child transmission. Based on current knowledge, the risk of transmission through vaginal or anal intercourse involving the use of a condom has been judged to be minimal, provided that the person infected with HIV fulfils the criteria for effective ART. This probably also applies to unprotected intercourse, provided that no other sexually transmitted infections are present, although it is not currently possible to fully support this conclusion with direct scientific evidence. ART is judged to markedly reduce the risk of blood-borne transmission between people who share injection equipment. Finally, the risk of transmission from mother to child is very low, provided that ART is started well in advance of delivery.
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| 2. |
- Bengtsson, Linus, et al.
(författare)
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Implementation of Web-Based Respondent-Driven Sampling among Men Who Have Sex with Men in Vietnam
- 2012
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:11, s. e49417-
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Lack of representative data about hidden groups, like men who have sex with men (MSM), hinders an evidence-based response to the HIV epidemics. Respondent-driven sampling (RDS) was developed to overcome sampling challenges in studies of populations like MSM for which sampling frames are absent. Internet-based RDS (webRDS) can potentially circumvent limitations of the original RDS method. We aimed to implement and evaluate webRDS among a hidden population. Methods and Design: criteria were men, aged 18 and above, who had ever had sex with another man and were living in Vietnam. Participants were invited by an MSM friend, logged in, and answered a survey. Participants could recruit up to four MSM friends. We evaluated the system by its success in generating sustained recruitment and the degree to which the sample compositions stabilized with increasing sample size. Results: Twenty starting participants generated 676 participants over 24 recruitment waves. Analyses did not show evidence of bias due to ineligible participation. Estimated mean age was 22 years and 82% came from the two large metropolitan areas. 32 out of 63 provinces were represented. The median number of sexual partners during the last six months was two. The sample composition stabilized well for 16 out of 17 variables. Conclusion: Results indicate that webRDS could be implemented at a low cost among Internet-using MSM in Vietnam. WebRDS may be a promising method for sampling of Internet-using MSM and other hidden groups.
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| 3. |
- Bengtsson, Linus, et al.
(författare)
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Strong propensity for HIV transmission among men who have sex with men in Vietnam : behavioural data and sexual network modelling
- 2014
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Ingår i: BMJ Open. - : BMJ. - 2044-6055. ; 4:1
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Tidskriftsartikel (refereegranskat)abstract
- Objectives Survey data from men who have sex with men (MSM) in Asian cities indicate ongoing and drastic increases in HIV prevalence. It is unknown which behavioural factors are most important in driving these epidemics. We aimed to analyse detailed sexual behaviour data among MSM in Vietnam and to model HIV transmission using improved assumptions on sexual network structure. Setting Vietnam. Participants Internet-using men who had ever had sex (any type) with a man, aged 18years and living in Vietnam. The study was cross-sectional, population-based and performed in 2012, using online respondent-driven sampling. The Internet-based survey instrument was completed by 982 participants, of which 857 were eligible. Questions included sociodemography and retrospective sexual behaviour, including number of unprotected anal sex (UAS) acts per partner. Primary and secondary outcome measures Estimated basic reproductive number over 3months as a function of transmission risk per UAS act; frequency distributions of number of UAS partners and UAS acts during last 3months. Results 36% (CI 32% to 42%) reported UAS at least once during the last 3months. 36% (CI 32% to 41%) had ever taken an HIV test and received the result. UAS partner numbers and number of UAS acts were both highly skewed and positively correlated. Using a weighted configuration model, taking into account partner numbers, frequency of UAS and their correlations, we estimated the basic reproductive number (R0) over 3months. The results indicated rapid transmission over a wide range of values of per-act transmissibility. Conclusions Men with multiple partners had unexpectedly high UAS frequency per partner, paired with low HIV testing rates. The study highlights the importance of collecting data on frequency of UAS acts and indicates the need to rapidly scale-up HIV prevention services and testing opportunities for MSM in Vietnam.
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| 4. |
- Boman, Magnus, et al.
(författare)
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Social network visualization as a contract tracing tool
- 2006. - 1
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Konferensbidrag (refereegranskat)abstract
- Something many pathogens have in common is the requirement for tracing their spread under harsh time constraints, posing a so-called contact tracing (or ``race-to-trace'') problem. We present a tool for visualizing contact networks, an important step towards practical use by epidemiologists, which generates interactive three-dimensional (3D) network visualizations. Its general purpose visualization engine can support multiple applications and varying pathogens. The main purpose is to trace, in the case of an outbreak, contacts among individuals known to have been at the same place.
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| 5. |
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| 6. |
- Britton, Tom, et al.
(författare)
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A weighted configuration model and inhomogeneous epidemics
- 2011
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Ingår i: Journal of statistical physics. - : Springer Science and Business Media LLC. - 0022-4715 .- 1572-9613. ; 145, s. 1368-1384
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Tidskriftsartikel (refereegranskat)abstract
- A random graph model with prescribed degree distribution and degree dependent edge weights is introduced. Each vertex is independently equipped with a random number of half-edges and each half-edge is assigned an integer valued weight according to a distribution that is allowed to depend on the degree of its vertex. Half-edges with the same weight are then paired randomly to create edges. An expression for the threshold for the appearance of a giant component in the resulting graph is derived using results on multi-type branching processes. The same technique also gives an expression for the basic reproduction number for an epidemic on the graph where the probability that a certain edge is used for transmission is a function of the edge weight (reflecting how closely ‘connected’ the corresponding vertices are). It is demonstrated that, if vertices with large degree tend to have large (small) weights on their edges and if the transmission probability increases with the edge weight, then it is easier (harder) for the epidemic to take off compared to a randomized epidemic with the same degree and weight distribution. A recipe for calculating the probability of a large outbreak in the epidemic and the size of such an outbreak is also given. Finally, the model is fitted to three empirical weighted networks of importance for the spread of contagious diseases and it is shown that R0 can be substantially over- or underestimated if the correlation between degree and weight is not taken into account.
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| 7. |
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| 8. |
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| 9. |
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| 10. |
- Camitz, Martin, et al.
(författare)
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The effect of travel restrictions on the spread of a moderately contagious disease
- 2006
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Ingår i: BMC Medicine. - : Springer Science and Business Media LLC. - 1741-7015. ; 4, s. 32-
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Tidskriftsartikel (refereegranskat)abstract
- Background: Much research in epidemiology has been focused on evaluating conventional methods of control strategies in the event of an epidemic or pandemic. Travel restrictions are often suggested as an efficient way to reduce the spread of a contagious disease that threatens public health, but few papers have studied in depth the effects of travel restrictions. In this study, we investigated what effect different levels of travel restrictions might have on the speed and geographical spread of an outbreak of a disease similar to severe acute respiratory syndrome (SARS). Methods: We used a stochastic simulation model incorporating survey data of travel patterns between municipalities in Sweden collected over 3 years. We tested scenarios of travel restrictions in which travel over distances > 50 km and 20 km would be banned, taking into account different levels of compliance. Results: We found that a ban on journeys > 50 km would drastically reduce the speed and geographical spread of outbreaks, even when compliance is < 100%. The result was found to be robust for different rates of intermunicipality transmission intensities. Conclusion: This study supports travel restrictions as an effective way to mitigate the effect of a future disease outbreak.
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| 11. |
- Chen, Saran, et al.
(författare)
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Indirect inference of sensitive variables with peer network survey
- 2021
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Ingår i: Journal of Complex Networks. - : Oxford University Press (OUP). - 2051-1310 .- 2051-1329. ; 9:6
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Tidskriftsartikel (refereegranskat)abstract
- Misreporting is a common source of bias in population surveys involving sensitive topics such as sexual behaviours, abortion or criminal activity. To protect their privacy due to stigmatized or illegal behaviour, respondents tend to avoid fully disclosure of personal information deemed sensitive. This attitude however may compromise the results of survey studies. To circumvent this limitation, this article proposes a novel ego-centric sampling method (ECM) based on the respondent's peer networks to make indirect inferences on sensitive traits anonymously. Other than asking the respondents to report directly on their own behaviour, ECM takes into account the knowledge the respondents have about their social contacts in the target population. By using various scenarios and sensitive analysis on model and real populations, we show the high performance, that is low biases, that can be achieved using our method and the novel estimator. The method is also applied on a real-world survey to study traits of college students. This real-world exercise illustrates that the method is easy-to-implement, requiring few amendments to standard sampling protocols, and provides a high level of confidence on privacy among respondents. The exercise revealed that students tend to under-report their own sensitive and stigmatized traits, such as their sexual orientation. Little or no difference was observed in reporting non-sensitive traits. Altogether, our results indicate that ECM is a promising method able to encourage survey participation and reduce bias due to misreporting of sensitive traits through indirect and anonymous data collection.
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| 12. |
- Chen, Xiaolong, et al.
(författare)
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Nontrivial resource requirement in the early stage for containment of epidemics
- 2019
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Ingår i: Physical review. E. - 2470-0045 .- 2470-0053. ; 100:3
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Tidskriftsartikel (refereegranskat)abstract
- During epidemic control, containment of the disease is usually achieved through increasing a devoted resource to reduce the infectiousness. However, the impact of this resource expenditure has not been studied quantitatively. For disease spread, the recovery rate can be positively correlated with the average amount of resource devoted to infected individuals. By incorporating this relation we build a novel model and find that insufficient resource leads to an abrupt increase in the infected population size, which is in marked contrast with the continuous phase transitions believed previously. Counterintuitively, this abrupt phase transition is more pronounced in less contagious diseases. Furthermore, we find that even for a single infection source, the public resource needs to be available in a significant amount, which is proportional to the total population size, to ensure epidemic containment. Our findings provide a theoretical foundation for efficient epidemic containment strategies in the early stage.
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Dai, Bitao, et al.
(författare)
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Identifying influential nodes by leveraging redundant ties
- 2023
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Ingår i: Journal of Computational Science. - 1877-7503 .- 1877-7511. ; 69
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Tidskriftsartikel (refereegranskat)abstract
- Structure-based influential nodes identification is a long-term challenge in the study of complex networks. While global centrality-based approaches are generally considered to be more accurate and reliable, the requirements of complete network information and high computational complexity are hard to meet, limiting their applications in many practical scenarios. In addition, recent studies have highlighted the effect of cyclic structures introducing redundant paths in network connectivity and exaggerating the importance of traditional centrality measures. In this work, we develop a new centrality metric, called Multi-Spanning Tree-based Degree Centrality (MSTDC), to quantify node importance with linear complexity by leveraging redundant ties. MSTDC is calculated using the aggregation of degrees of a small number of spanning trees constructed with a few randomly selected root nodes. Experiments on synthetic and empirical networks reveal that MSTDC obtains superior performance than other benchmark network centralities in identifying influential nodes from the perspective of both maintaining network connectivity and maximizing spreading capacity. In addition, we find that MSTDC is extraordinarily effective in networks with high clustering coefficients. Our study provides novel insights into the role of redundant ties in network structural and functional analyses.
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| 17. |
- Danielsson, Erna, 1954-, et al.
(författare)
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Sociologiska perspektiv på coronakrisen : Fyra sociologer om samhällets reaktion på covid-19
- 2020
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Ingår i: Sociologisk forskning. - Annelöv : Sveriges sociologförbund. - 0038-0342 .- 2002-066X. ; 57:1, s. 67-76
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Sociologisk Forskning bad fyra sociologer i Sverige att svara på några korta frågor om coronapandemin och vårt samhälles hantering av den.Deras tidigare forskning har på olika sätt berört olika frågor såsom socialmedicin och medicinsk kunskapsproduktion, sociala nätverks betydelse för smittspridning, samhällets hantering av kriser och risker, genusaspekter av samhällskriser samt dynamiken mellan expertis, politiker och medborgare i beslutsfattande och debatter kring frågor där expertkunskap är centralt. Utifrån svaren på frågorna redigerade tidskriftens redaktörer en sammanhängande text, som de fyra forskarna sedan kunde ändra och göra tillägg i. Resultatet är en gemensam text som påminner om ett samtal. Den slutliga texten färdigställdes den 8 april 2020 .De fyra medverkande forskarna är Erna Danielsson, docent i sociologi vid Mittuni-versitetet och föreståndare för Risk and Crisis Research Centre (RCR), som forskar om samhällets krishantering vid såväl vardagskriser som större händelser och specifikt genus och krishantering; Fredrik Liljeros, professor i sociologi vid Stockholms universitet, som genomförde sitt postdoktorprojekt på dåvarande Smittskyddsinstitutet tillsammans med nuvarande statsepidemiologen Anders Tegnell och i dag bedriver forskning om hur människors kontaktnätverk påverkar spridningsdynamik; Shai Mulinari, docent i sociologi vid Lunds universitet, som bedriver forskning om medicinsk kunskapsproduktion, läkemedelsindustrin, epidemiologi och folkhälsa; samt Linda Soneryd, professor i sociologi vid Göteborgs universitet, som forskat om miljörelaterade risker och kriser samt om hur demokrati och deltagande förstås i anslutning till expertfrågor.
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| 18. |
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| 19. |
- Edling, Christofer, et al.
(författare)
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Social skiktning
- 2010
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Ingår i: Ett delat samhälle. - Malmö : Liber. - 9789147090426 ; , s. 8-30
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 20. |
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Ett delat samhälle : makt, intersektionalitet och social skiktning
- 2010. - 1. uppl.
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- Sociologin har ända sedan ämnets grundande sysslat med samma problemställning: Hur ska vi förstå samhällets sociala ojämlikhet och hur påverkar den människors livschanser? Men trots denna gemensamma kärna, finns det inom sociologin en mångfald av teoretiska perspektiv, metodologiska ansatser och olika sätt att se samhället. I denna antologi visar författarna att sociologins pluralism inte ska ses som en svaghet, utan snarare som en tillgång som berikar ämnet. De vill ge en inblick i sociologins djup och bredd – och på så sätt inspirera till fortsatt sociologiskt tänkande!
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| 21. |
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| 22. |
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Ett delat samhälle - makt, intersektionalitet och social skiktning, 3e uppl.
- 2022
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- Boken ger en inblick i sociologins djup och bredd genom att inspirera till fortsatt tänkande om det delade samhället. I den tredje upplagan har flera kapitel reviderats och boken har utökats med ett nyskrivet kapitel om regionala och geografiska skillnader för att ge ökad förståelse av ojämlikhet och förändring mellan stad och land och inom storstadsregionerna.Sedan sociologin grundades har ämnet sysslat med samma problemställning: Hur ska vi förstå samhällets sociala ojämlikhet och hur påverkar den människors livschanser? Utifrån denna gemensamma kärna har sociologin utvecklat en mångfald av teoretiska perspektiv och metodologiska ansatser för att se samhället.
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| 23. |
- Fridlund, Veronika, 1980-
(författare)
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Play with fire, play with you sometimes : Social aspects of condom use among young people in Sweden
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although Sweden invests a great deal of money and effort in prevention work, STIs are a major problem in our society. Young people are at high risk both when it comes to unwanted pregnancies and STIs and several studies have revealed that the condom use is quite low. Condom use is a complex issue. There are often several factors that interact and affect the decision to use or not use condom. The result in this thesis shows that young people have behavioral expectation to use condom, especially for anal sex and vaginal sex with a casual partner (both known and unknown). At the same time, the condom use is low irrespective of type of partner and type of sex. Approximately 20 % of the participants never used a condom during the preceding 12 months. Most of the participants said that reason for their use or non-use was based on partner evaluation. However, our participants indicate that there often is a deeper reason why they do not use condoms. Women talk about their male partner’s resistance against condom use. Men in the other hand mention the problem with fit and feel especially problems related to erection problems when they have been drinking alcohol. One of the most interesting findings is that the participants’ view of sex affected their condom use. Those with a relaxed view (e.g., did not connect love with sex and had had more sexual partners during the past 12 months) had fewer occasions of unprotected vaginal intercourse compared with the participants with a traditional view (e.g., often associated sex with vaginal penetration).The most important thing we need to do is increase ’men’s sense of responsibility and involve them in the prevention work. It is also important that the condom counseling is individualized. It is not enough to simply speak about condom use in general; instead we need to relate condom use to sexual practice and partner type but also to the individuals’ specific condom problem.
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| 24. |
- Gallos, Lazaros K., et al.
(författare)
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How People Interact in Evolving Online Affiliation Networks
- 2012
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Ingår i: Physical Review X. - 2160-3308. ; 2:3, s. 031014-
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Tidskriftsartikel (refereegranskat)abstract
- The study of human interactions is of central importance for understanding the behavior of individuals, groups, and societies. Here, we observe the formation and evolution of networks by monitoring the addition of all new links, and we analyze quantitatively the tendencies used to create ties in these evolving online affiliation networks. We show that an accurate estimation of these probabilistic tendencies can be achieved only by following the time evolution of the network. Inferences about the reason for the existence of links using statistical analysis of network snapshots must therefore be made with great caution. Here, we start by characterizing every single link when the tie was established in the network. This information allows us to describe the probabilistic tendencies of tie formation and extract meaningful sociological conclusions. We also find significant differences in behavioral traits in the social tendencies among individuals according to their degree of activity, gender, age, popularity, and other attributes. For instance, in the particular data sets analyzed here, we find that women reciprocate connections 3 times as much as men and that this difference increases with age. Men tend to connect with the most popular people more often than women do, across all ages. On the other hand, triangular tie tendencies are similar, independent of gender, and show an increase with age. These results require further validation in other social settings. Our findings can be useful to build models of realistic social network structures and to discover the underlying laws that govern establishment of ties in evolving social networks.
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| 25. |
- Gallos, Lazaros K, et al.
(författare)
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Improving immunization strategies.
- 2007
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Ingår i: Phys Rev E Stat Nonlin Soft Matter Phys. - 1539-3755. ; 75:4 Pt 2, s. 045104-
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Tidskriftsartikel (refereegranskat)
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| 26. |
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| 27. |
- Halvarsson, Veronika, et al.
(författare)
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The prescription of oral contraceptives and its relation to the incidence of chlamydia and abortion in Sweden 1997-2005
- 2012
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Ingår i: Scandinavian Journal of Public Health. - : SAGE Publications. - 1403-4948 .- 1651-1905. ; 40:1, s. 85-91
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Tidskriftsartikel (refereegranskat)abstract
- Aims: The aim of this study is to examine the association between the prescription of oral contraceptives and the incidence of chlamydia, and between the prescription of oral contraceptives and the number of abortions in a population-based ecological study. Methods: For this study we used register data from the Swedish Institute for Infectious Disease Control (chlamydia incidence), the Swedish National Board of Health and Welfare (number of abortions), Statistics Sweden (population data), and Apoteket (Swedish pharmacy) (prescriptions for oral contraceptives). We conducted ordinary least squares regression analysis of the association between chlamydia or abortions and the prescription of oral contraceptives. Results: The prescription of oral contraceptives has a positive association on both the incidence of chlamydia and the numbers of abortion. Our best model predicts that prescription of 100 yearly doses of oral contraceptives increase the abortions by 3.3 cases among 16-year-old women and 0.7 cases among 29-year-old women, while cases of chlamydia increase by 6.7 among 16-year-old women and 1.5 among 29-year-old women. Conclusions: Our findings indicate that the use of oral contraceptives among young people and young adults is positively associated with the chlamydia incidence and the abortion rate in these populations in Sweden.
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| 28. |
- Hansson, Disa
(författare)
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Hidden desires : Modelling sexual behaviour and the spread of sexually transmitted infections
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis we use statistical and mathematical models to study different sexual behaviours of relevance for the spread of sexually transmitted infections (STIs). Two groups of special interest for STI interventions are considered: sexually active youths and men who have sex with men (MSM). The focus of the first paper is on mechanisms giving rise to the observed condom use and anal sex behaviour among young people in Sweden. We study the sexual dispositions of individuals, how these interact and generate the observed sexual outcome. The second paper concerns the sexual behaviour of MSM in Sweden and the transmission process of HIV within this population. The population is modelled by a stochastic dynamic network which incorporates both steady partnerships and casual contacts. We model the spread of an infection where individuals are susceptible, infectious, or diagnosed (and unable to transmit) and derive the basic reproduction number R0, the probability of a major outbreak and the endemic prevalence.
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| 29. |
- Hansson, Disa, et al.
(författare)
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Inferring individual sexual action dispositions from egocentric network data on dyadic sexual outcomes
- 2018
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 13:11
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a family of models that allows us to estimate egos' unobserved action dispositions from a joint behavioural outcome of a dyadic social interaction process of both egos' and alters' action dispositions. The method is put to test on a data set containing two different types of dyadic activities of high relevance for the spread of sexually transmitted infections (STI), condom use and anal sex. The data consists of individuals older than 15 years old who visited one of the nine youth clinics in the Vastra Gotaland region of Sweden between February 2010 and March 2011 for STI testing. This is hence a group of special interest for STI interventions. We cannot find any difference in condom disposition between women and men. Condoms are initially used more often in less risky types of relationships, especially if the partner ends up as a main partner. When studying the disposition towards anal sex we do however find a difference between men and women. Women are more against practising anal sex than men while the majority of men are neutral towards anal sex.
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| 30. |
- Hansson, Disa, 1986-
(författare)
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Modelling Sexual Interactions : Sexual behaviour and the spread of sexually transmitted infections on dynamic networks
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis we develop statistical and mathematical models to study different factors of relevance for the spread of sexually transmitted infections (STIs). Two special interest groups for STI interventions are considered: sexually active youths and men who have sex with men (MSM). The statistical models developed make it possible to estimate individuals’ dispositions towards sexual behaviours related to the spread of STIs: condom use and anal sex. To study the spread of an infection in a population we use mathematical models. The mathematical models in this thesis give insights into the transmission process of HIV among MSM in Sweden—a population at high risk for HIV infection.The focus of the first paper is on mechanisms giving rise to observed sexual behaviour, such as condom use, among sexually active youths in Sweden. We study the sexual dispositions of individuals and how these interact and generate the observed sexual outcomes.The second paper concerns the sexual behaviour of MSM in Sweden and the transmission process of HIV within this population. The population is modelled by a stochastic dynamic network model that incorporates both steady partnerships and casual contacts. We model the spread of an infection where individuals are susceptible, infectious or diagnosed (unable to transmit) and derive the basic reproduction number R0, the probability of a major outbreak, and the endemic prevalence.The third paper further develops the dynamic network model of the second paper. The model now takes into account that individuals may be sexually high-active or sexually low-active. The division into two activity groups makes it possible to study a preventive intervention against HIV that is only targeted to sexually high-active. The intervention studied is pre-exposure prophylaxis for HIV (PrEP), i.e. that the antiviral drugs tenofovir-emtricitabine are taken by individuals with negative HIV serostatus to prevent getting infected by HIV. We study the PrEP coverage needed to reduce the observed HIV prevalence of 5% to a value close to 0%.In the fourth and final paper we focus on condom dispositions among MSM. The disposition models from the first paper are extended to better fit an MSM population and are additionally extended to be used for more types of sexual behaviour data.
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| 31. |
- Holme, Petter, 1973-, et al.
(författare)
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Birth and death of links control disease spreading in empirical contact networks
- 2014
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 4, s. 4999-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate what structural aspects of a collection of twelve empirical temporal networks of human contacts are important to disease spreading. We scan the entire parameter spaces of the two canonical models of infectious disease epidemiology-the Susceptible-Infectious-Susceptible (SIS) and Susceptible-Infectious-Removed (SIR) models. The results from these simulations are compared to reference data where we eliminate structures in the interevent intervals, the time to the first contact in the data, or the time from the last contact to the end of the sampling. The picture we find is that the birth and death of links, and the total number of contacts over a link, are essential to predict outbreaks. On the other hand, the exact times of contacts between the beginning and end, or the interevent interval distribution, do not matter much. In other words, a simplified picture of these empirical data sets that suffices for epidemiological purposes is that links are born, is active with some intensity, and die.
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| 32. |
- Holme, Petter, et al.
(författare)
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Mechanistic models in computational social science
- 2015
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Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 3
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Forskningsöversikt (refereegranskat)abstract
- Quantitative social science is not only about regression analysis or, in general, data inference. Computer simulations of social mechanisms have an over 60 years long history. They have been used for many different purposes to test scenarios, to test the consistency of descriptive theories (proof-of-concept models), to explore emergent phenomena, for forecasting, etc... In this essay, we sketch these historical developments, the role of mechanistic models in the social sciences and the influences from the natural and formal sciences. We argue that mechanistic computational models form a natural common ground for social and natural sciences, and look forward to possible future information flow across the social-natural divide.
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| 33. |
- Holme, Petter, et al.
(författare)
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Network bipartivity
- 2003
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1063-651X .- 1095-3787. ; 68:5 Pt 2
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Tidskriftsartikel (refereegranskat)abstract
- Systems with two types of agents with a preference for heterophilous interaction produce networks that are more or less close to bipartite. We propose two measures quantifying the notion of bipartivity. The two measures-one well known and natural, but computationally intractable, and the other computationally less complex, but also less intuitive-are examined on model networks that continuously interpolate between bipartite graphs and graphs with many odd circuits. We find that the bipartivity measures increase as we tune the control parameters of the test networks to intuitively increase the bipartivity, and thus conclude that the measures are quite relevant. We also measure and discuss the values of our bipartivity measures for empirical social networks (constructed from professional collaborations, Internet communities, and field surveys). Here we find, as expected, that networks arising from romantic online interaction have high, and professional collaboration networks have low, bipartivity values. In some other cases, probably due to low average degree of the network, the bipartivity measures cannot distinguish between romantic and friendship oriented interaction.
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| 34. |
- Holme, Petter, et al.
(författare)
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Network Bipartivity
- 2003
-
Ingår i: Physical Review E. - 1063-651X. ; 68:5, s. 056107-
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Tidskriftsartikel (refereegranskat)
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| 35. |
- Karlsson, Magnus, et al.
(författare)
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Ålder
- 2010
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Ingår i: Ett delat samhälle. - 9789147090426 ; , s. 119-145
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Bokkapitel (refereegranskat)
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| 36. |
- Karlsson, Magnus, et al.
(författare)
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Ålder
- 2016. - 2
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Ingår i: Ett delat samhälle : makt, intersektionalitet och social skiktning - makt, intersektionalitet och social skiktning. - 9789147112821 ; , s. 119-149
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Bokkapitel (populärvet., debatt m.m.)
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| 37. |
- Kitsak, Maksim, et al.
(författare)
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Identification of influential spreaders in complex networks
- 2010
-
Ingår i: Nature Physics. - 1745-2473 .- 1745-2481. ; 6:11, s. 888-893
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Tidskriftsartikel (refereegranskat)abstract
- Networks portray a multitude of interactions through which people meet, ideas are spread and infectious diseases propagate within a society(1-5). Identifying the most efficient 'spreaders' in a network is an important step towards optimizing the use of available resources and ensuring the more efficient spread of information. Here we show that, in contrast to common belief, there are plausible circumstances where the best spreaders do not correspond to the most highly connected or the most central people(6-10). Instead, we find that the most efficient spreaders are those located within the core of the network as identified by the k-shell decomposition analysis(11-13), and that when multiple spreaders are considered simultaneously the distance between them becomes the crucial parameter that determines the extent of the spreading. Furthermore, we show that infections persist in the high-k shells of the network in the case where recovered individuals do not develop immunity. Our analysis should provide a route for an optimal design of efficient dissemination strategies.
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| 38. |
- Klingvall, Mikael, 1971-
(författare)
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Adaptability or Efficiency : Towards a theory of institutional development in organizations
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Organizations, once established, tend not to change, typically going obsolete as society continues to evolve. This makes adaptability an important issue. Organizational members must make sense to each other, or coordination suffers. They must also make sense to environmental actors, or the organization will not achieve the support it needs to survive. This sense-making is a process of institutionalization, of constructing a shared understanding of the organization's enterprise, business and environment. When environmental actors adopt new priorities, ideas and modes of thinking, organizations must develop a new understanding of reality or go obsolete. To stay adaptable, organizations needs to contain competing perspectives. But the pressures to conform and to coordinate make it difficult for established organizations to adapt, trapped by the very benefits of increased efficiency. Using an agent-based model of organizational institutionalization, I show that an organization's adaptability is highly dependent on structural elements that affect the member interaction frequencies, and that organizations that leverage the strength of weak ties between member groups can maintain adaptability. The effects of changes to any of these elements are decidedly non-linear, however, which helps explain why it is difficult to design effective organizations. Organizational structure is one part of a tri-partite framework of institutional development in organizations and of organizational adaptability, where the other two parts are the individual characteristics of the members and the content of the organizational culture.
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| 39. |
- Lee, Sungmin, et al.
(författare)
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Exploiting Temporal Network Structures of Human Interaction to Effectively Immunize Populations
- 2012
-
Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:5, s. e36439-
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Tidskriftsartikel (refereegranskat)abstract
- Decreasing the number of people who must be vaccinated to immunize a community against an infectious disease could both save resources and decrease outbreak sizes. A key to reaching such a lower threshold of immunization is to find and vaccinate people who, through their behavior, are more likely than average to become infected and to spread the disease further. Fortunately, the very behavior that makes these people important to vaccinate can help us to localize them. Earlier studies have shown that one can use previous contacts to find people that are central in static contact networks. However, real contact patterns are not static. In this paper, we investigate if there is additional information in the temporal contact structure for vaccination protocols to exploit. We answer this affirmative by proposing two immunization methods that exploit temporal correlations and showing that these methods outperform a benchmark static-network protocol in four empirical contact datasets under various epidemic scenarios. Both methods rely only on obtainable, local information, and can be implemented in practice. For the datasets directly related to contact patterns of potential disease spreading ( of sexually-transmitted and nosocomial infections respectively), the most efficient protocol is to sample people at random and vaccinate their latest contacts. The network datasets are temporal, which enables us to make more realistic evaluations than earlier studies-we use only information about the past for the purpose of vaccination, and about the future to simulate disease outbreaks. Using analytically tractable models, we identify two temporal structures that explain how the protocols earn their efficiency in the empirical data. This paper is a first step towards real vaccination protocols that exploit temporal-network structure-future work is needed both to characterize the structure of real contact sequences and to devise immunization methods that exploit these.
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| 40. |
- Lee, Sungmin, 1975-, et al.
(författare)
-
Exploiting temporal network structures of human interaction to effectively immunize populations
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- If we can lower the number of people needed to vaccinate for a community to be immune against contagious diseases, we can save resources and life. A key to reach such a lower threshold of immunization is to find and vaccinate people who, through their behavior, are more likely to become infected and effective to spread the disease than the average. Fortunately, the very behavior that makes these people important to vaccinate can help us finding them. People you have met recently are more likely to be socially active and thus central in the contact pattern, and important to vaccinate. We propose two immunization schemes exploiting temporal contact patterns. Both of these rely only on obtainable, local information and could implemented in practice. We show that these schemes outperform benchmark protocols in four real data sets under various epidemic scenarios. The data sets are dynamic, which enables us to make more realistic evaluations than other studies - we use information only about the past to perform the vaccination and the future to simulate disease outbreaks. We also use models to elucidate the mechanisms behind how the temporal structures make our immunization protocols efficient.
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| 41. |
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| 42. |
- Liljeros, Fredrik
(författare)
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Sociala simuleringar
- 2004
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Ingår i: Sociologisk forskning. - : Sveriges Sociologförbund. - 0038-0342 .- 2002-066X. ; 41:2, s. 19-22
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 43. |
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| 44. |
- Liljeros, Fredrik, et al.
(författare)
-
The contact network of inpatients in a regional healthcare system. A longitudinal case study
- 2007
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Ingår i: Mathematical Population Studies. - : Informa UK Limited. - 0889-8480 .- 1547-724X. ; 14:4, s. 269-284
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Tidskriftsartikel (refereegranskat)abstract
- Contact networks are extracted for 295,108 inpatients over a two-year period from a database used for administering a local public healthcare system that serves 1.8 million individuals in Stockholm county. Structural and dynamic properties of the network that are important for the transmission of contagious diseases are analyzed by methods derived from network epidemiology. The contact networks are found to be very much determined by an extreme (age-independent) variation in the duration of hospital stays and the hospital structure. The structure of contacts between inpatients are found to exhibit structural properties such as a high level of transitivity, assortativity, and variation by number of contacts, which are likely to be of importance for the transmission of less contagious diseases. If these properties are considered when designing prevention programs, the risk and effect of epidemic outbreaks may be decreased.
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| 45. |
- Liljeros, Fredrik, et al.
(författare)
-
The web of human sexual contacts.
- 2001
-
Ingår i: Nature. - 0028-0836. ; 411:6840, s. 907-8
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
|
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| 46. |
- Lu, Xin, et al.
(författare)
-
Respondent-driven sampling on directed networks
- 2013
-
Ingår i: Electronic Journal of Statistics. - 1935-7524. ; 7, s. 292-322
-
Tidskriftsartikel (refereegranskat)abstract
- Respondent-driven sampling (RDS) is a widely used method for generating chain-referral samples from hidden populations. It is an extension of the snowball sampling method and can, given that some assumptions are met, generate unbiased population estimates. One key assumption, not likely to be met, is that the acquaintance network in which the recruitment process takes place is undirected, meaning that all recruiters should have the potential to be recruited by the person they recruit. Using a mean-field approach, we develop an estimator which is based on prior information about the average indegrees of estimated variables. When the indegree is known, such as for RDS studies over internet social networks, the estimator can greatly reduce estimate error and bias as compared with current methods; when the indegree is not known, which is most common for interview-based RDS studies, the estimator can through sensitivity analysis be used as a tool to account for uncertainties of network directedness and error in self-reported degree data. The performance of the new estimator, together with previous RDS estimators, is investigated thoroughly by simulations on networks with varying structures. We have applied the new estimator on an empirical RDS study for injecting drug users in New York City.
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| 47. |
- Lu, Xin, et al.
(författare)
-
The sensitivity of respondent-driven sampling
- 2012
-
Ingår i: Journal of the Royal Statistical Society. - 0964-1998 .- 1467-985X. ; 175:1, s. 191-216
-
Tidskriftsartikel (refereegranskat)abstract
- Researchers in many scientific fields make inferences from individuals to larger groups. For many groups, however, there is no list of members from which to draw a random sample. Respondent-driven sampling (RDS) is a relatively new sampling methodology that circumvents this difficulty by using the social networks of the groups under study. The RDS method has been shown to provide unbiased estimates of population proportions given certain conditions. The method is now widely used in human immunodeficiency virus related studies among high risk populations globally. We test the RDS methodology by simulating RDS studies on the social networks of a large Lesbian, gay, bisexual and transgender Web community. The robustness of the RDS method is tested by violating, one by one, the conditions under which the method provides unbiased estimates. Simulations indicate that the bias is large if networks are directed or respondents choose to invite people on the basis of characteristics that are correlated with the study outcomes. The bias and variance increase if participants invite close as opposed to more distant friends whereas sampling in denser networks sharply reduces variance. However, the RDS method shows strong resistance to sampling without replacement, low response rates and certain errors in the participants reporting of their network sizes, as well as the selection criteria of seeds. The effects of network structure and the number of seeds and coupons are also discussed.
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| 48. |
- Malmros, Jens, et al.
(författare)
-
Respondent-driven sampling and an unusual epidemic
- 2016
-
Ingår i: Journal of Applied Probability. - : Cambridge University Press (CUP). - 0021-9002 .- 1475-6072. ; 53:2, s. 518-540
-
Tidskriftsartikel (refereegranskat)abstract
- Respondent-driven sampling (RDS) is frequently used when sampling from hidden populations. In RDS, sampled individuals pass on participation coupons to at most c of their acquaintances in the community (c = 3 being a common choice). If these individuals choose to participate, they in turn pass coupons on to their acquaintances, and so on. The process of recruiting is shown to behave like a new Reed-Frost-type network epidemic, in which `becoming infected' corresponds to study participation. We calculate R-0, the probability of a major `outbreak', and the relative size of a major outbreak for c < infinity in the limit of infinite population size and compare to the standard Reed-Frost epidemic. Our results indicate that c should often be chosen larger than in current practice.
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| 49. |
- Malmros, Jens
(författare)
-
Some advances in Respondent-driven sampling on directed social networks
- 2013
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Respondent-driven sampling (RDS) is one of the most commonly used methods when sampling from hidden or hard-to-reach populations. The RDS methodology combines an improved snowball sampling scheme with a mathematical model that is able to produce unbiased population estimates given that some assumptions about the actual recruitment process are fulfilled. One critical assumption, which is not likely to hold in most cases, is that the underlying social network of the population is undirected. The papers in this thesis provide extensions of RDS theory to populations with partially directed social networks.
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| 50. |
- Malmros, Jens, 1980-
(författare)
-
Studies in respondent-driven sampling : Directed networks, epidemics, and random walks
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Respondent-driven sampling (RDS) is a link-tracing sampling methodology especially suitable for sampling hidden populations. A clever sampling mechanism and inferential procedures that facilitate asymptotically unbiased population estimates has contributed to the rising popularity of the method. The papers in this thesis extend RDS estimation theory to some population structures to which the classical RDS estimation framework is not applicable and analyse the behaviour of the RDS recruitment process.
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