Omission Bias

Concept and classic experiments

Spranca, Minsk and Baron (1991) presented participants with cases in which the outcome was the same but harm resulted from acting in one case and from failing to act in the other. For example, a person who deliberately recommended a food to someone with an allergy was blamed more than one who knowingly failed to stop that person from eating it. Even with intent and outcome held equal, many participants rated commission as worse. Ritov and Baron (1990) showed the tendency in vaccination decisions: even when the risk of death from disease exceeded the risk from vaccine side effects, many participants weighted harm from vaccinating more heavily and were reluctant to vaccinate. Asch and colleagues (1994) reported similar tendencies among parents who had actually decided about pertussis vaccination for their children.

Why it happens

Kahneman and Miller's (1986) norm theory holds that people evaluate outcomes by bringing to mind alternatives that might have happened. Outcomes produced by departing from the default through action readily evoke the thought "if only I hadn't," generating stronger regret and responsibility. Gilovich and Medvec (1995) concluded that people regret actions more in the short term but inactions more in the long term, showing that the relationship between regret and omission can shift over time. Ritov and Baron (1992) reported that although omission bias often overlaps with status quo bias, experimental separation reveals a distinct preference for omission itself. Baron and Ritov (2004) also showed large individual differences in the strength of the bias.

Moral judgment and policy

Omission bias is a major topic in research on moral judgment. Cushman, Young and Hauser (2006) reported that people can articulate, relatively consciously, an action principle under which harm caused by action is worse than harm caused by omission. The tendency appears clearly in thought experiments such as the trolley dilemma, which asks whether to act and sacrifice one person or do nothing and let five be harmed. In policy, harm resulting from introducing a new program tends to attract more blame than harm from maintaining an existing one, and this has been cited as a reason reforms are delayed. Researchers continue to debate how far the moral distinction between acts and omissions is legitimate and where it becomes a bias.

FAQ

What is omission bias in simple terms?

It is the tendency to see a bad result caused by doing something as worse than the same bad result caused by doing nothing. As a result, people often choose to stay passive, where they feel less responsible.

Is omission bias the same as status quo bias?

They are similar but not identical. Status quo bias is a preference for not changing the current state; omission bias is a preference for not acting. They often overlap because keeping the status quo usually means doing nothing, but experiments can separate the two.

Sources reviewed: 2026-10-26

References

1. Spranca, M., Minsk, E., & Baron, J. (1991). Omission and commission in judgment and choice. Journal of Experimental Social Psychology, 27(1), 76–105. The core set of experiments comparing harmful acts and omissions — the basic evidence in one place.
2. Ritov, I., & Baron, J. (1990). Reluctance to vaccinate: Omission bias and ambiguity. Journal of Behavioral Decision Making, 3(4), 263–277. Uses vaccination choices to show the bias in a concrete decision — good for seeing it in real-world choices.
3. Ritov, I., & Baron, J. (1992). Status-quo and omission biases. Journal of Risk and Uncertainty, 5(1), 49–61. Disentangles status quo bias from omission bias — read this if the two concepts blur together.
4. Kahneman, D., & Miller, D. T. (1986). Norm theory: Comparing reality to its alternatives. Psychological Review, 93(2), 136–153. Lays out norm theory — why outcomes of action feel more mutable — the psychological backdrop to omission bias.
5. Gilovich, T., & Medvec, V. H. (1995). The experience of regret: What, when, and why. Psychological Review, 102(2), 379–395. Shows people regret actions more in the short term but inactions more in the long run — useful on regret and omission.
6. Baron, J., & Ritov, I. (2004). Omission bias, individual differences, and normality. Organizational Behavior and Human Decision Processes, 94(2), 74–85. Examines individual differences in the bias — helpful for seeing that not everyone shows it equally.
7. Cushman, F., Young, L., & Hauser, M. (2006). The role of conscious reasoning and intuition in moral judgment: Testing three principles of harm. Psychological Science, 17(12), 1082–1089. Tests the action/omission principle among three moral principles — a bridge to trolley-style moral judgment.
8. Asch, D. A., Baron, J., Hershey, J. C., Kunreuther, H., Meszaros, J., Ritov, I., & Spranca, M. (1994). Omission bias and pertussis vaccination. Medical Decision Making, 14(2), 118–123. Surveys real parents' pertussis vaccine decisions — evidence that the bias shows up outside the lab.