| 1. |
- Eriksson, Henrik, et al.
(författare)
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Words with intervening neighbours in infinite Coxeter groups are reduced
- 2010
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Ingår i: The Electronic Journal of Combinatorics. - : The Electronic Journal of Combinatorics. - 1097-1440 .- 1077-8926. ; 17:1, s. N9-
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Tidskriftsartikel (refereegranskat)abstract
- Consider a graph with vertex set S. A word in the alphabet S has the intervening neighbours property if any two occurrences of the same letter are separated by all its graph neighbours. For a Coxeter graph, words represent group elements. Speyer recently proved that words with the intervening neighbours property are reduced if the group is infinite and irreducible. We present a new and shorter proof using the root automaton for recognition of reduced words.
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| 2. |
- Andrén, Lina J., 1980-
(författare)
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On Latin squares and avoidable arrays
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis consists of the four papers listed below and a survey of the research area. I Lina J. Andrén: Avoiding (m, m, m)-arrays of order n = 2k II Lina J. Andrén: Avoidability of random arrays III Lina J. Andr´en: Avoidability by Latin squares of arrays with even order IV Lina J. Andrén, Carl Johan Casselgren and Lars-Daniel Öhman: Avoiding arrays of odd order by Latin squares Papers I, III and IV are all concerned with a conjecture by Häggkvist saying that there is a constant c such that for any positive integer n, if m ≤ cn, then for every n × n array A of subsets of {1, . . . , n} such that no cell contains a set of size greater than m, and none of the elements 1, . . . , n belongs to more than m of the sets in any row or any column of A, there is a Latin square L on the symbols 1, . . . , n such that there is no cell in L that contains a symbol that belongs to the set in the corresponding cell of A. Such a Latin square is said to avoid A. In Paper I, the conjecture is proved in the special case of order n = 2k . Paper III improves on the techniques of Paper I, expanding the proof to cover all arrays of even order. Finally, in Paper IV, similar methods are used together with a recoloring theorem to prove the conjecture for all orders. Paper II considers another aspect of the problem by asking to what extent way a deterministic result concerning the existence of Latin squares that avoid certain arrays can be used when the sets in the array are assigned randomly.
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| 3. |
- Bernard, Mark, et al.
(författare)
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The subgroup problem : When can binding voting on extractions from a common pool resource overcome the tragedy of the commons?
- 2013
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Ingår i: Journal of Economic Behavior and Organization. - : Elsevier BV. - 0167-2681 .- 1879-1751. ; 91, s. 122-130
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Tidskriftsartikel (refereegranskat)abstract
- Using a common pool resource game protocol with voting we examine experimentally how cooperation varies with the level at which (binding) votes are aggregated. Our results are broadly in line with theoretical predictions. When players can vote on the behavior of the whole group or when leaders from each group can vote for the group as a whole, extraction levels from the common resource pool are close to the social optimum. When players extract resources individually, there is substantial overextraction. When players vote in subgroups, there is initially less overextraction but it increases over time. This suggests that in order for binding voting to overcome the tragedy of the commons in social dilemmas, it should ideally affect the group as a whole.
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| 4. |
- Bernard, Mark, et al.
(författare)
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The subgroup problem: When can binding voting on extractions from a common resource pool overcome the tragedy of the commons?
- 2013
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Ingår i: Journal of Economic Behavior and Organization. - : Elsevier BV. - 0167-2681 .- 1879-1751. ; 91, s. 122-130
-
Tidskriftsartikel (refereegranskat)abstract
- Using a common pool resource game protocol with voting we examine experimentally how cooperation varies with the level at which (binding) votes are aggregated. Our results are broadly in line with theoretical predictions. When players can vote on the behavior of the whole group or when leaders from each group can vote for the group as a whole, extraction levels from the common resource pool are close to the social optimum. When players extract resources individually, there is substantial overextraction. When players vote in subgroups, there is initially less overextraction but it increases over time. This suggests that in order for binding voting to overcome the tragedy of the commons in social dilemmas, it should ideally affect the group as a whole.
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| 5. |
- de Barra, Mícheál, et al.
(författare)
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How feedback biases give ineffective medical treatments a good reputation.
- 2014
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Ingår i: Journal of medical Internet research. - : JMIR Publications Inc.. - 1438-8871. ; 16:8, s. e193-
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Medical treatments with no direct effect (like homeopathy) or that cause harm (like bloodletting) are common across cultures and throughout history. How do such treatments spread and persist? Most medical treatments result in a range of outcomes: some people improve while others deteriorate. If the people who improve are more inclined to tell others about their experiences than the people who deteriorate, ineffective or even harmful treatments can maintain a good reputation.OBJECTIVE: The intent of this study was to test the hypothesis that positive outcomes are overrepresented in online medical product reviews, to examine if this reputational distortion is large enough to bias people's decisions, and to explore the implications of this bias for the cultural evolution of medical treatments.METHODS: We compared outcomes of weight loss treatments and fertility treatments in clinical trials to outcomes reported in 1901 reviews on Amazon. Then, in a series of experiments, we evaluated people's choice of weight loss diet after reading different reviews. Finally, a mathematical model was used to examine if this bias could result in less effective treatments having a better reputation than more effective treatments.RESULTS: Data are consistent with the hypothesis that people with better outcomes are more inclined to write reviews. After 6 months on the diet, 93% (64/69) of online reviewers reported a weight loss of 10 kg or more while just 27% (19/71) of clinical trial participants experienced this level of weight change. A similar positive distortion was found in fertility treatment reviews. In a series of experiments, we show that people are more inclined to begin a diet with many positive reviews, than a diet with reviews that are representative of the diet's true effect. A mathematical model of medical cultural evolution shows that the size of the positive distortion critically depends on the shape of the outcome distribution.CONCLUSIONS: Online reviews overestimate the benefits of medical treatments, probably because people with negative outcomes are less inclined to tell others about their experiences. This bias can enable ineffective medical treatments to maintain a good reputation.
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| 6. |
- Ehn, Micael
(författare)
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Modeling Specialization and Division of Labor in Cultural Evolution
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Division of labor and division of knowledge are so important and common in society today that it is difficult to imagine a functional society where everyone knows the same things and performs the same tasks. In such a society everyone grows, or gathers, and prepares their own food, makes their own tools, builds their own house, and so on. Cultural evolution is the field of research that studies the creation and diffusion of ideas and societies. It is very uncommon for these studies to take into account the effects of specialization. This thesis will show that specialization is of great importance to cultural evolution. The thesis is divided into two parts: The first is an introduction to studies of specialization and division of labor. The thesis begins with an interdisciplinary survey of the research on division of labor and specialization, including both theoretic and empirical studies. Next is an introduction to modeling specialization and division of labor. This includes a general framework and a number of basic models of different aspects of specialization and division of labor. Part two consists of four papers. The first paper studies the interaction between specialization and cultural cumulation. The second and third papers examine cultural cumulation, specifically the circumstances under which cultural knowledge increases and how cultural knowledge is distributed in the population. The last paper is a mathematical model of how specialization of knowledge (i.e. higher education) leads to social stratification.
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| 7. |
- Enquist, Magnus, 1955-, et al.
(författare)
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Modelling the evolution and diversity of cumulative culture
- 2011
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 366:1563, s. 412-423
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Tidskriftsartikel (refereegranskat)abstract
- Previous work on mathematical models of cultural evolution has mainly focused on the diffusion of simple cultural elements. However, a characteristic feature of human cultural evolution is the seemingly limitless appearance of new and increasingly complex cultural elements. Here, we develop a general modelling framework to study such cumulative processes, in which we assume that the appearance and disappearance of cultural elements are stochastic events that depend on the current state of culture. Five scenarios are explored: evolution of independent cultural elements, stepwise modification of elements, differentiation or combination of elements and systems of cultural elements. As one application of our framework, we study the evolution of cultural diversity (in time as well as between groups).
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| 8. |
- Enquist, Magnus, et al.
(författare)
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One cultural parent makes no culture
- 2010
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Ingår i: Animal Behaviour. - : Elsevier BV. - 0003-3472 .- 1095-8282. ; 79:6, s. 1353-1362
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Tidskriftsartikel (refereegranskat)abstract
- The ability to acquire knowledge and skills from others is widespread in animals and is commonly thought to be responsible for the behavioural traditions observed in many species. However, in spite of the extensive literature on theoretical analyses and empirical studies of social learning, little attention has been given to whether individuals acquire knowledge from a single individual or multiple models. Researchers commonly refer to instances of sons learning from fathers, or daughters from mothers, while theoreticians have constructed models of uniparental transmission, with little consideration of whether such restricted modes of transmission are actually feasible. We used mathematical models to demonstrate that the conditions under which learning from a single cultural parent can lead to stable culture are surprisingly restricted ( the same reasoning applies to a single social-learning event). Conversely, we demonstrate how learning from more than one cultural parent can establish culture, and find that cultural traits will reach a nonzero equilibrium in the population provided the product of the fidelity of social learning and the number of cultural parents exceeds 1. We discuss the implications of the analysis for interpreting various findings in the animal social-learning literature, as well as the unique features of human culture.
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| 9. |
- Eriksson, Kimmo, 1967-
(författare)
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A Note on the Exact Expected Length of the kth Part of a Random Partition
- 2010
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Ingår i: Integers. - 1867-0652. ; 10, s. 309-311
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Tidskriftsartikel (refereegranskat)abstract
- Kessler and Livingstone proved an asymptotic formula for the expected length of the largest part of a partition drawn uniformly at random. As a first step they gave an exact formula expressed as a weighted sum of Euler's partition function. Here we give a short bijective proof of a generalization of this exact formula to the expected length of the kth part.
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| 10. |
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