Leadership,consensus decision making and collective behaviour in humans

This paper reviews the literature on leadership in vertebrate groups, including recent work on human groups, before presenting the results of three new experiments looking at leadership and decision making in small and large human groups. In experiment 1, we find that both group size and the presence of uninformed individuals can affect the speed with which small human groups (eight people) decide between two opposing directional preferences and the likelihood of the group splitting. In experiment 2, we show that the spatial positioning of informed individuals within small human groups (10 people) can affect the speed and accuracy of group motion. We find that having a mixture of leaders positioned in the centre and on the edge of a group increases the speed and accuracy with which the group reaches their target. In experiment 3, we use large human crowds (100 and 200 people) to demonstrate that the trends observed from earlier work using small human groups can be applied to larger crowds. We find that only a small minority of informed individuals is needed to guide a large uninformed group. These studies build upon important theoretical and empirical work on leadership and decision making in animal groups.     

Accurate decisions in an uncertain world: collective cognition increases true positives while decreasing false positives

In a wide range of contexts, including predator avoidance, medical decision-making and security screening, decision accuracy is fundamentally constrained by the trade-off between true and false positives. Increased true positives are possible only at the cost of increased false positives; conversely, decreased false positives are associated with decreased true positives. We use an integrated theoretical and experimental approach to show that a group of decision-makers can overcome this basic limitation. Using a mathematical model, we show that a simple quorum decision rule enables individuals in groups to simultaneously increase true positives and decrease false positives. The results from a predator-detection experiment that we performed with humans are in line with these predictions: (i) after observing the choices of the other group members, individuals both increase true positives and decrease false positives, (ii) this effect gets stronger as group size increases, (iii) individuals use a quorum threshold set between the average true- and false-positive rates of the other group members, and (iv) individuals adjust their quorum adaptively to the performance of the group. Our results have broad implications for our understanding of the ecology and evolution of group-living animals and lend themselves for applications in the human domain such as the design of improved screening methods in medical, forensic, security and business applications.     

Quorum sensing by encounter rates in the ant Temnothorax albipennis

Emigrating colonies of the ant Temnothorax (formerly Leptothorax)albipennis can choose the best of several nest sites, even whenthe active ants organizing the move do not compare sites. Thiscollective ability depends on a quorum rule used by ants assessinga candidate site. Only when the site's population has surpasseda threshold do they switch from slow recruitment of fellow activeants by tandem runs to rapid transport of the majority of thecolony. Here, I show that ants perceive the achievement of aquorum through their rate of direct encounters with nest matesat the site. When ants in a crowded site were prevented fromtactile contact with nest mates, they recruited by tandem runs,as though to an empty nest. Furthermore, when the encounterrate was raised independent of population, by reducing the sizeof the candidate nest, ants started to transport at a significantlylower population. The switch occurred at the same encounterrate regardless of nest size, whether the rate was measuredas the mean over the entire visit or as the inverse of the latencyuntil the first encounter. Because encounter rate reflects thedensity of nest mates and thus varies with nest size as wellas population, the ants' collective decision-making algorithmmay be robust to the exact population at which the switch totransport occurs. Ants cease monitoring quorum presence afterswitching to transport, coincident with an abrupt shorteningof visit duration by approximately 2 min, which may be interpretedas the time required for quorum detection.     

高等医学院校行政成本控制系统评估初探

降低行政成本对高等医学院校及其附属医院的可持续发展具有重要意义,引入成本控制系统是一个有前景的解决方案。基于TOPSIS方法建立了评估成本控制系统的数学模型,实例表明建立的数学模型简单有效,有助于定量决策。     

Comprehensive criteria for biodiversity evaluation in conservation planning

In this paper we present the results of a multi-criteria decision analysis used to identify a comprehensive set of criteria for assigning biodiversity value to sites for conservation planning. For effective conservation management, biodiversity value needs to be a composite of biotic and abiotic factors. However, in the reserve design literature, conservation value is assigned with a limited set of metrics usually based on comprehensiveness, representativeness and persistence which may be insufficient at fully capturing biodiversity value. A group of conservation specialists in California, USA, used a multi-criteria decision making framework to elucidate and weight criteria for scoring biodiversity value at sites. A formal model for consensus and negotiation was applied to aggregate individuals’ criteria weights across all group members. The group identified ecological condition, followed by biotic composition as the most important contributors to site conservation value. Long- and short-term threats causing fragmentation and degradation are also important criteria to consider. Key criteria are identified for which further data collection would serve the greatest purpose in prioritizing sites and the role of prioritization criteria in the larger context of systematic conservation planning is discussed. With the recognition that biodiversity value plays an important role in conservation decisions, the criteria presented here represents a comprehensive suite of factors to consider when assigning biodiversity value to sites for conservation planning. These can serve as an encompassing list which other groups can customize for the purpose of biodiversity evaluation for alternative conservation planning contexts.