In everyday life, people encounter smaller rewards with higher probability than larger rewards. Do people expect this reward-probability regularity to hold in experimental settings? To answer this question, we tested whether people's behavior in probability judgment tasks is affected by the correlation between reward size and reward probabilities. In Study 1, we asked people to judge reward probabilities under uncertainty. In line with the ecological reward-probability correlation, people assumed that larger rewards were less likely than smaller rewards. In Study 2, we tested the prediction that people's information search and integration depend on the representativeness of the environment. Participants performed an experience-based probability judgment task in which they sampled outcomes from unknown gambles until they felt confident to estimate the probabilities of the gambles' outcomes. We manipulated the reward-probability relationship of the gambles in 3 experimental groups. Rewards and reward probabilities were negatively correlated, positively correlated, or not correlated at all. A negative correlation mimics the ecological reward-probability relationship often present in real life. We analyzed people's search effort and whether they integrated sample-based uncertainty into their judgments. We found that people sampled fewer outcomes in the ecologically representative condition than in the other 2 conditions. However, people did not integrate sample-based uncertainty in their judgments: In all conditions people treated the observed outcomes as representative of the underlying outcome distribution. People's prior beliefs about regularities in environments provides a potential explanation of why people often rely on small sample sizes when making judgments and decisions from experience. (PsycINFO Database Record

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People often learn from experience about the distribution of outcomes of risky options. Typically, people draw small samples, when they can actively sample information from risky gambles to make decisions. We examine how the size of the sample that people experience in decision from experience affects their preferences between risky options. In two studies ( N = 40 each), we manipulated the size of samples that people could experience from risky gambles and measured subjective selling prices and the confidence in selling price judgements after sampling. The results show that, on average, sample size influenced neither the selling prices nor confidence. However, cognitive modelling of individual-level learning showed that around half of the participants could be classified as Bayesian learners, whereas the other half adhered to a frequentist learning strategy and that if learning was cognitively simpler more participants adhered to the latter. The observed selling prices of Bayesian learners changed with sample size as predicted by Bayesian principles, whereas sample size affected the judgements of frequentist learners much less. These results illustrate the variability in how people learn from sampled information and provide an explanation for why sample size often does not affect judgements.

In clinical trials, incentivizing human research subjects with large amounts of money is often considered unethical, as it may coerce people to participate. This argument implies that people perceive rewards (i.e., incentives) independently of risks (i.e., probability of side-effects) or that they assume that larger rewards are associated with lower risks. However, past research on risk perception indicates that people associate higher rewards with higher risks. To test whether people treat incentives in clinical trials as a proxy for risk, we conducted an online experiment (N = 483) in which people estimated the riskiness of hypothetical clinical trials. We manipulated the monetary incentives that participants of the clinical trials were offered. The results show that people expect more side effects if the monetary incentives for participation are higher. Results further show that the majority of participants were more likely to ethically approve a trial if it offered a high monetary incentive. In contrast to existing ethical guidelines these results suggest that paying large rewards may be less problematic because people implicitly associate them with higher risk and because they trade-off risks and financial benefits.

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