Sterchi, Martin

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Martin
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Sterchi, Martin

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2018 - 201952020 - 20235
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  • Vorschaubild
    Publikation
    Active querying approach to epidemic source detection on contact networks
    (Nature, 2023) Sterchi, Martin; Hilfiker, Lorenz; Grütter, Rolf; Bernstein, Abraham [in: Scientific Reports]
    The problem of identifying the source of an epidemic (also called patient zero) given a network of contacts and a set of infected individuals has attracted interest from a broad range of research communities. The successful and timely identification of the source can prevent a lot of harm as the number of possible infection routes can be narrowed down and potentially infected individuals can be isolated. Previous research on this topic often assumes that it is possible to observe the state of a substantial fraction of individuals in the network before attempting to identify the source. We, on the contrary, assume that observing the state of individuals in the network is costly or difficult and, hence, only the state of one or few individuals is initially observed. Moreover, we presume that not only the source is unknown, but also the duration for which the epidemic has evolved. From this more general problem setting a need to query the state of other (so far unobserved) individuals arises. In analogy with active learning, this leads us to formulate the active querying problem. In the active querying problem, we alternate between a source inference step and a querying step. For the source inference step, we rely on existing work but take a Bayesian perspective by putting a prior on the duration of the epidemic. In the querying step, we aim to query the states of individuals that provide the most information about the source of the epidemic, and to this end, we propose strategies inspired by the active learning literature. Our results are strongly in favor of a querying strategy that selects individuals for whom the disagreement between individual predictions, made by all possible sources separately, and a consensus prediction is maximal. Our approach is flexible and, in particular, can be applied to static as well as temporal networks. To demonstrate our approach’s practical importance, we experiment with three empirical (temporal) contact networks: a network of pig movements, a network of sexual contacts, and a network of face-to-face contacts between residents of a village in Malawi. The results show that active querying strategies can lead to substantially improved source inference results as compared to baseline heuristics. In fact, querying only a small fraction of nodes in a network is often enough to achieve a source inference performance comparable to a situation where the infection states of all nodes are known.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild nicht verfügbar
    Publikation
    Covid-19 superspreading. lessons from simulations on an empirical contact network
    (2021) Hilfiker, Lorenz; Sterchi, Martin
    Infectious individuals who cause an extraordinarily large number of secondary infections are colloquially referred to as superspreaders. Their pivotal role for the transmission of Covid-19 has been exemplified by now infamous cases such as the Washington choir practice, where one infectious individual caused 52 secondary infections [1]. In order to formally analyse superspreading, we denote by Z the individual reproduction number. In a fully susceptible population, the mean mZ is known as the basic reproduction number R0. Based on branching arguments and assuming a well-mixed population, the distribution of Z is typically modelled by a negative binomial distribution whose variance mZ(1+mZ=kZ) is characterised by the dispersion parameter kZ [2]. Empirical evidence suggests that Covid-19 exhibits a particularly wide distribution of Z, with the right tail representing superspreading events. In situations without interventions, the dispersion parameter kZ was estimated in the range 0.04 - 0.2 [3, 4]. Some studies even found evidence for a fat tailed Z-distribution, possibly a power law with the exponent close to 1 [5, 6]. The underlying mechanisms for the emergence of this level of heterogeneity are difficult to establish. A priori, network effects could play a role, as suggested in [5]. A more frequent line of reasoning focuses on physiological or biological factors: wet pronunciation, loud speech, frequent coughing or higher viral loads could result in some infected individuals being inherently more prone to spread the disease than others during an encounter with a susceptible individual [7]. Combining both lines of thought, the study in [8] shows that individual variation in infectiousness indeed leads to higher variance of Z on some standard static network models. However, no previous study has investigated heterogeneities of the Z-distribution on empirical contact networks. Therefore, we provide preliminary simulation results based on one realistic temporal social contact network and gather further evidence that the key to finding Z-distributions in alignment with empirical data is to allow for individual variation in infectiousness.
    06 - Präsentation
  • Vorschaubild
    Publikation
    Outbreak detection for temporal contact data
    (Springer, 2021) Sterchi, Martin; Sarasua, Cristina; Grütter, Rolf; Bernstein, Abraham [in: Applied Network Science]
    Epidemic spreading is a widely studied process due to its importance and possibly grave consequences for society. While the classical context of epidemic spreading refers to pathogens transmitted among humans or animals, it is straightforward to apply similar ideas to the spread of information (e.g., a rumor) or the spread of computer viruses. This paper addresses the question of how to optimally select nodes for monitoring in a network of timestamped contact events between individuals. We consider three optimization objectives: the detection likelihood, the time until detection, and the population that is affected by an outbreak. The optimization approach we use is based on a simple greedy approach and has been proposed in a seminal paper focusing on information spreading and water contamination. We extend this work to the setting of disease spreading and present its application with two example networks: a timestamped network of sexual contacts and a network of animal transports between farms. We apply the optimization procedure to a large set of outbreak scenarios that we generate with a susceptible-infectious-recovered model. We find that simple heuristic methods that select nodes with high degree or many contacts compare well in terms of outbreak detection performance with the (greedily) optimal set of nodes. Furthermore, we observe that nodes optimized on past periods may not be optimal for outbreak detection in future periods. However, seasonal effects may help in determining which past period generalizes well to some future period. Finally, we demonstrate that the detection performance depends on the simulation settings. In general, if we force the simulator to generate larger outbreaks, the detection performance will improve, as larger outbreaks tend to occur in the more connected part of the network where the top monitoring nodes are typically located. A natural progression of this work is to analyze how a representative set of outbreak scenarios can be generated, possibly taking into account more realistic propagation models.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild nicht verfügbar
    Publikation
    MeteoSwiss CHAPo: pollen information needs analysis
    (Fachhochschule Nordwestschweiz FHNW, 2021) Fuduric, Nikolina; Kraft, Corin; Sterchi, Martin
    There is a network of pollen measurement devices in 14 stations throughout Switzerland. To date, the standard of pollen identification and measurement has been done manually with calculations and models providing forecasts with a six day delay. This standard is not serving the allergic public, the doctors and scientists specializing in pollen research any longer. A laser technology measurement device has successfully been tested in the regional center of MeteoSwiss in Payerne. It opens up new perspectives in terms of automation, real-time transmission and higher data quality. The technology is not only applicable to pollen measurement, but also enables partnerships to be strengthened in the areas of air quality and health effects. Based on this technology, MeteoSwiss can provide new, more valuable data products and services. With these new possibilities, two questions arise which are explored in this research report: Q1) What data products and services best serve the allergic public and doctors? Q2) Within which channels should these products be offered? MeteoSwiss has invited the University of Applied Sciences Northwestern Switzerland's (FHNW) School of Business to conduct a needs analysis of the two above-mentioned target groups. The needs analysis was carried out using a customer insights research-based method called “Jobs to Be Done” (JtbD) originally from Harvard University (Christensen 1997). The FHNW researchers extrapolated those jobs or tasks that were important to the target groups but not satisfied in the market. Upon isolating these “jobs”, MeteoSwiss experts from the CHAPo project and aha! were invited to design workshops at the FHNW to create a rough prototype of data products based on the research outcomes.
    05 - Forschungs- oder Arbeitsbericht
  • Vorschaubild nicht verfügbar
    Publikation
    Maximizing the likelihood of detecting outbreaks in temporal networks
    (Springer, 2020) Sterchi, Martin; Sarasua, Cristina; Grütter, Rolf; Bernstein, Abraham; Cherifi, Hocine; Gaito, Sabrina; Mendes, José Fernendo; Moro, Esteban; Rocha, Luis Mateus [in: Complex networks and their applications VIII. Volume 2 proceedings of the eighth international conference on complex networks and their applications. Complex Networks 2019]
    Epidemic spreading occurs among animals, humans, or computers and causes substantial societal, personal, or economic losses if left undetected. Based on known temporal contact networks, we propose an outbreak detection method that identifies a small set of nodes such that the likelihood of detecting recent outbreaks is maximal. The two-step procedure involves (i) simulating spreading scenarios from all possible seed configurations and (ii) greedily selecting nodes for monitoring in order to maximize the detection likelihood. We find that the detection likelihood is a submodular set function for which it has been proven that greedy optimization attains at least 63% of the optimal (intractable) solution. The results show that the proposed method detects more outbreaks than benchmark methods suggested recently and is robust against badly chosen parameters. In addition, our method can be used for outbreak source detection. A limitation of this method is its heavy use of computational resources. However, for large graphs the method could be easily parallelized.
    04B - Beitrag Konferenzschrift
  • Vorschaubild
    Publikation
    The pig transport network in Switzerland. Structure, patterns, and implications for the transmission of infectious diseases between animal holdings
    (Public Library of Science, 2019) Sterchi, Martin; Faverjon, Céline; Sarasua, Cristina; Vargas, Maria Elena; Berezowski, John; Bernstein, Abraham; Grütter, Rolf; Nathues, Heiko [in: PLOS ONE]
    The topology of animal transport networks contributes substantially to how fast and to what extent a disease can transmit between animal holdings. Therefore, public authorities in many countries mandate livestock holdings to report all movements of animals. However, the reported data often does not contain information about the exact sequence of transports, making it impossible to assess the effect of truck sharing and truck contamination on disease transmission. The aim of this study was to analyze the topology of the Swiss pig transport network by means of social network analysis and to assess the implications for disease transmission between animal holdings. In particular, we studied how additional information about transport sequences changes the topology of the contact network. The study is based on the official animal movement database in Switzerland and a sample of transport data from one transport company. The results show that the Swiss pig transport network is highly fragmented, which mitigates the
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild nicht verfügbar
    Publikation
    Unreliable is better: theoretical and practical impulses for performance management
    (Nomos, 2019) Stöckli, Sabrina; Messner, Claude; Sterchi, Martin; Dorn, Michael [in: Die Unternehmung]
    This review aims to stimulate discussion about a comprehensive understanding of performance evaluation – namely, the taken-for granted benefit of maximal reliable performance evaluation, where employee performance is evaluated with high levels of reliability (i.e., large samples of performance observations). So far, the management discipline has ignored the evidence-based view that one’s performance is better under unreliable performance evaluation compared to reliable performance evaluation. Drawing on tournament theory, behavioral research, and real-world sports data, we argue that while reliable performance evaluation boosts only superior employees, unreliable performance evaluation boosts all employees. The mechanisms that drive inferior and superior employees to perform better when evaluated unreliably substantiate that psychological insight is essential for efficient performance management. Overall, we complement the predominant thinking of performance management by offering innovative insights and implications that are significant for academics, employees, and employers.
    01B - Beitrag in Magazin oder Zeitung
  • Vorschaubild
    Publikation
    A transdisciplinary approach supporting the implementation of a big data project in livestock production: an example from the Swiss pig production industry
    (Frontiers Research Foundation, 2019) Faverjon, Céline; Bernstein, Abraham; Grütter, Rolf; Nathues, Christina; Nathues, Heiko; Sarasua, Cristina; Sterchi, Martin; Vargas, Maria Elena; Berezowski, John [in: Frontiers in Veterinary Science]
    Big Data approaches offer potential benefits for improving animal health, but they have not been broadly implemented in livestock production systems. Privacy issues, the large number of stakeholders, and the competitive environment all make data sharing, and integration a challenge in livestock production systems. The Swiss pig production industry illustrates these and other Big Data issues. It is a highly decentralized and fragmented complex network made up of a large number of small independent actors collecting a large amount of heterogeneous data. Transdisciplinary approaches hold promise for overcoming some of the barriers to implementing Big Data approaches in livestock production systems. The purpose of our paper is to describe the use of a transdisciplinary approach in a Big Data research project in the Swiss pig industry. We provide a brief overview of the research project named “Pig Data,” describing the structure of the project, the tools developed for collaboration and knowledge transfer, the data received, and some of the challenges. Our experience provides insight and direction for researchers looking to use similar approaches in livestock production system research.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild
    Publikation
    A survey-based design of a pricing system for psychotherapy
    (BioMed Central, 2018) Hulliger, Beat; Sterchi, Martin [in: Health Economics Review]
    Erstellung eines Tarifs für Leistungserbringer im Gesundheitswesen, psychologische Psychotherapeuten, aufgrund einer Erhebung über Kosten der Psychotherapie und einer Erhebung über Zeitaufwände für die Psychotherapie.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild nicht verfügbar
    Publikation
    PIG DATA. Transdisciplinary approach for health analytics of the Swiss Swine Industry
    (2018) Sterchi, Martin
    Combining big data methods and transdisciplinary approaches for providing sustainable solutions for real-time decision making in the Swiss Swine Industry.
    06 - Präsentation