Base-rate neglect, the tendency of adults to ignore the prior probability of an event, has been well-studied over the past decades. However, the evidence for base-rate neglect and its theoretical implications are still debated. We argue that such lack of agreement comes from the mistaken assumption that performance unequivocally reflects cognitive processes. We adopt a different viewpoint, namely that performance reflects existing constraints in the person-task relation. To test whether this viewpoint is appropriate for performance in base-rate problems we manipulated the constraints available in the task’s response options. With a highly constraining response mode adults are expected to exhibit the classic base-rate neglect, with little variability in their performance as procedural factors are manipulated. However, with a less constraining response mode performance is expected to be more variable and more susceptible to subtle changes in the task procedure. Results support this view, demonstrating non-linear context effects in decision making.