Computer simulations and two experiments are reported to delineate the ultimate sampling dilemma, which constitutes a serious obstacle to inductive inferences in a probabilistic world. Participants were asked to take the role of a manager who is to make purchasing decisions based on positive versus negative feedback about three providers in two different product domains. When information sampling (from a computerized data base) was over, they had to make inferences about actual differences in the data base from which the sample was drawn (e.g., about the actual superiority of different providers, or about the most likely origins of negatively valenced products). The ultimate sampling dilemma consists in a forced choice between two search strategies that both have their advantages and their drawbacks: natural sampling and deliberate sampling of information relevant to the inference task. Both strategies leave the sample unbiased for specific inferences but create errors or biases for other inferences. Many everyday decision problems rely on direct environmental-learning experience.Teachers' grading decisions are informed by observations of students' performance in different disciplines. Personnel selection relies on applicants' reactions to various tasks and interview topics. Or, consumer choices reflect the information acquired about brands or providers in different product domains. There appears to be a simple and straightforward way of optimizing such experience-based decisions: If only the learning process relies on a sufficiently large sample of observations, it must be possible to discern the optimal decision through optimal data selection (Oaksford & Chater, 2003).The learning task seems to have a clear-cut structure. For a consumer to make an optimal choice between alternative providers, it is only necessary to compare the quality feedback that is available for different providers in specific product domains. Granting that the feedback is reliable and accurately reflects the contingency between providers and product quality, figuring out the best provider, with the highest rate of positive evaluations, should be straightforward. The consumer's task should be easy to solve if only the differences between providers are strong enough and sufficient observations are available.The aim of the present investigation is to contest this seemingly plausible sketch of simple experience-based decision making. In fact, finding a generally correct solution to such clearly structured problems is fraught with huge difficulties. It is actually impossible, because every sample of observations about mundane decision problems entails the potential to be misleading under certain conditions. I refer to the "ultimate sampling dilemma" to highlight the fact that any reasonable sampling strategy, which serves to optimize one decision, produces a sampling bias with regard to other decisions informed by the same data.
Illustration of the Ultimate Sampling DilemmaThat judgments and decisions depend crucially on the samples of...