This research investigated whether people are more likely to attribute events to external agents when events are negative rather than neutral or positive. Participants more often believed that ultimatum game partners were humans rather than computers when the partners offered unusually unfavorable divisions than unusually favorable divisions (Experiment 1A), even when their human partners had no financial stake in the game (Experiment 1B). In subsequent experiments, participants were most likely to infer that gambles were influenced by an impartial participant when the outcomes of those gambles were losses rather than wins (Experiments 2 and 3), despite their explicitly equal probability. The results suggest a negative agency bias--negative events are more often attributed to the influence of external agents than similarly positive and neutral events, independent of their subjective probability.

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