We present a traffic analysis of the ADU anonymity scheme presented at ESORICS 2008, and the related RADU scheme. We show that optimal attacks are able to de-anonymize messages more effectively than believed before. Our analysis applies to single messages as well as long term observations using multiple messages. The search of a “better” scheme is bound to fail, since we prove that the original...

It is often claimed that opinions are more likely to be correct if they are held independently by many individuals. But what does it mean to hold independent opinions? To clarify this condition, we distinguish four notions of probabilistic opinion independence. Which notion applies depends on environmental factors such as commonly perceived evidence. More formally, it depends on the causal netw...

Previous studies have shown that one can exploit “wisdom of crowds” by oneself. This is achieved by aggregating multiple “quasi-independent” estimates from the same person. However, previous methods were not necessarily easy to utilize. Therefore, we propose an efficient method based on perspective-taking. The procedure is as follows: First, one makes her/his own estimation. Second, one estimat...

Statistical aggregation is often used to combine multiple opinions within a group. Such aggregates outperform individuals, including experts, in various prediction and estimation tasks. This result is attributed to the "wisdom of crowds". We seek to improve the quality of such aggregates by identifying and eliminating poor performing individuals from the crowd. We propose a new measure of contr...

Classic examples of service disasters include Victoria’s Secrets and the NASA Pathfinder mission web casts, during which users could not access to the sites or experienced infinite delays. These were caused by the so-called Flash Crowds [8], which are large numbers of users trying to access the same web site simultaneously and thus demanding site resources exponentially. The issue further compl...

Crowd-Computer Interaction CCI is a form of human-computer interaction HCI in which single actions from many individuals are aggregated to produce a different result that would not be achievable otherwise for one individual alone. As a research topic several questions remain open regarding CCI, for example, to what extent the principles and heuristics of interactions design under the paradigm o...

This paper evaluates an automatic technique for detection of abnormal events in crowds. Crowd behaviour is difficult to predict and might not be easily semantically translated. Moreover it is difficult to track individuals in the crowd using state of the art tracking algorithms. Therefore we characterise crowd behaviour by observing the crowd optical flow and use unsupervised feature extraction...

Estimating and forecasting are difficult tasks. This is true whether the activity requires the determination of uncertain future event outcomes, or whether the estimation effort is complex in itself and based on insufficient information. Consequently, such tasks are frequently assigned to experts. Surprisingly, recent research suggests that collectives of non-experts can outperform individual e...

We introduce and test a crowdsourcing technique for creative problem solving. In total, 1853 workers from Amazon’s Mechanical Turk produced 468 ideas for solving the 2010 oil spill problem in the Gulf of Mexico. In our technique, one crowd generated initial ideas, another crowd evaluated the creativity of these ideas, and yet another crowd combined pairs of ideas produced by the previous crowd....