We consider crowdsourcing problems where the users are asked to provide evaluations for items; the user evaluations are then used directly, or aggregated into a consensus value. Lacking an incentive scheme, users have no motive in making effort in completing the evaluations, providing inaccurate answers instead. We propose incentive schemes that are truthful and cheap: truthful as the optimal user behavior consists in providing accurate evaluations, and cheap because the truthfulness is achieved with little overhead cost. We consider both discrete evaluation tasks, where an evaluation can be done either correctly, or incorrectly, with no degrees of approximation in between, and quantitative evaluation tasks, where evaluations are real numbers, and the error is measured as distance from the correct value. For both types of tasks, we propose hierarchical incentive schemes that can be effected with a small amount of additional evaluations, and that scale to arbitrarily large crowd sizes: they have the property that the strength of the incentive does not weaken with increasing hierarchy depth. Interestingly, we show that for these schemes to work, the only requisite is that workers know their place in the hierarchy in advance.
Prediction markets are models with a goal of obtaining predictions about events of interest from experts. After experts provide predictions, a system assigns a reward based on a scoring rule to every expert. Proper scoring rules ensure that the highest reward is achieved by reporting the true probability distribution @cite_13 @cite_0 @cite_20 . An assumption of the scoring rules is that the future outcome must be observable. This assumption prevents crowdsourcing systems to scale to large crowds as obtaining the correct answer for each event or task is prohibitively expensive.
@cite_0 @cite_13 @cite_20
1599628716 2194444479 2187708490 2130782832
In practice, scoring rules elicit good probability estimates from individuals, while betting markets elicit good consensus estimates from groups. Market scoring rules combine these features, eliciting estimates from individuals or groups, with groups costing no more than individuals. Regarding a bet on one event given another event, only logarithmic versions preserve the probability of the given event. Logarithmic versions also preserve the conditional probabilities of other events, and so preserve conditional independence relations. Given logarithmic rules that elicit relative probabilities of base event pairs, it costs no more to elicit estimates on all combinations of these base events. We report the results of the first large-scale, long-term, experimental test between two crowd sourcing methods – prediction markets and prediction polls. More than 2,400 participants made forecasts on 261 events over two seasons of a geopolitical prediction tournament. Some forecasters traded in a continuous double auction market and were ranked based on earnings. Others submitted probability judgments, independently or in teams, and were ranked based on Brier scores. In both seasons of the tournament, last day prices from the prediction market were more accurate than the simple mean of forecasts from prediction polls. However, team prediction polls outperformed prediction markets when poll forecasts were aggregated with algorithms using temporal decay, performance weighting and recalibration. The biggest advantage of prediction polls occurred at the start of long-duration questions. Prediction polls with proper scoring, algorithmic aggregation and teaming offer an attractive alternative to prediction markets for distilling the wisdom of crowds. Prediction markets are economic mechanisms for aggregating information about future events through sequential interactions with traders. The pricing mechanisms in these markets are known to be related to optimization algorithms in machine learning and through these connections we have some understanding of how equilibrium market prices relate to the beliefs of the traders in a market. However, little is known about rates and guarantees for the convergence of these sequential mechanisms, and two recent papers cite this as an important open question. In this paper we show how some previously studied prediction market trading models can be understood as a natural generalization of randomized coordinate descent which we call randomized subspace descent (RSD). We establish convergence rates for RSD and leverage them to prove rates for the two prediction market models above, answering the open questions. Our results extend beyond standard centralized markets to arbitrary trade networks. Prediction markets are used in real life to predict outcomes of interest such as presidential elections. In this work we introduce a mathematical theory for Artificial Prediction Markets for supervised classifier aggregation and probability estimation. We introduce the artificial prediction market as a novel way to aggregate classifiers. We derive the market equations to enforce total budget conservation, show the market price uniqueness and give efficient algorithms for computing it. We show how to train the market participants by updating their budgets using training examples. We introduce classifier specialization as a new differentiating characteristic between classifiers. Finally, we present experiments using random decision rules as specialized classifiers and show that the prediction market consistently outperforms Random Forest on real and synthetic data of varying degrees of difficulty.