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Two experiments on the process of rule discovery in groups were conducted using a card deck and Wason number triple tasks. The positive effects of incentives on the proportion of correct hypotheses could not be explained by differential testing. The variables “hypothesis vs. target testing” and “small vs. broad range of rule” did not affect this proportion. There was a preponderance of positive tests, declining during trials. Negative tests occurred more often under the target test and broad rule range conditions. The positivity heuristic diminished in importance during trials, whereas the sufficiency, necessity, and Klayman and Ha heuristics increased. Groups produced fewer false and more correct results than individuals. According to the probabilistic model of opinion change, plausibility and faction size contributed to the group process differentially, depending on the task.