Online collaborative projects in which users contribute to extensive knowledge bases such as Wikipedia or OpenStreetMap have become increasingly popular while yielding highly accurate information.Collaboration in such projects is organized sequentially with one contributor creating an entry and the following contributors deciding whether to adjust or to maintain the presented information.We refer to this process as sequential collaboration since individual judgments directly depend on the previous judgment.As sequential collaboration has not yet been examined systematically, we investigate whether dependent, sequential judgments become increasingly more accurate.Moreover, we test whether final sequential judgments are more accurate than the unweighted average of independent judgments from equally large groups.We conducted three studies with groups of four to six contributors who either answered general knowledge questions (Experiments 1 and 2) or located cities on maps (Experiment 3).As expected, individual judgments became more accurate across the course of sequential chains and final estimates were similarly accurate as unweighted averaging of independent judgments.These results show that sequential collaboration profits from dependent, incremental judgments, thereby shedding light on the contribution process underlying large-scale online collaborative projects.

Using an advice-taking paradigm, we investigated how people use information about the wisdom of the crowds when revising their judgments.We focused on two types of information: information about the size of the advisor crowd and information about the distribution of the judgments within the crowd.To test whether judges use these two types of information, we varied the size of the advisor crowd (two, four, or eight advisors) and orthogonally manipulated whether judges received advice in the form of a crowd estimate or in the form of the separate individual judgments.In a third condition, participants received the crowd estimate, but it was labeled as stemming from an individual.We found no evidence that judges used information about the size of the crowd, but they considered information about the distribution of the advice when revising their opinions.Compared with crowd estimates, receiving the individual judgments as advice led to less advice taking but not to substantial differences in post-advice accuracy.Exploratory analyses showed that judges receiving multiple pieces of advice heeded advice less when their initial judgments were closer to the center of the distribution of judgments.In those instances, their initial judgments were also the most accurate, so they stood to gain less from the advice.Receiving multiple pieces of advice also led to smaller confidence gains, suggesting that judges receiving crowd judgments as advice might underestimate the variance of the underlying individual judgments.

Magic is an art form that allows us to experience the impossible, but some magic tricks are more implausible than others. We present two experiments that examined whether the objective probability of a trick occurring by chance influences how people experience the trick. In Experiment 1, participants watched different versions of a magic trick in which we manipulated the statistical probability of the trick occurring by chance. We found that the objective probability had no significant impact on how much people enjoyed the trick or how impressed they were by it. Our participants enjoyed the trick equally when there was a 25% chance of it succeeding by chance as when it was virtually impossible. The same was true for how impressed they were by the performance. However, tricks that were less likely to succeed by chance were rated as more difficult and impossible. More implausible tricks resulted in more participant explanations stating they did not know how the trick was done, as well as explanations implying it was fake. In a follow-up experiment, participants were presented with vignettes describing the same trick, and they were asked to judge the magician’s chances of succeeding. The statistical probability of the trick occurring by chance did not affect these judgments adversely, but they did do so when the same feat was performed by a nonmagician.