PsychologicalDUAL-USE

Omission Bias

What it is

The tendency to judge harmful actions as worse, and more blameworthy, than equally or more harmful inactions — so that doing nothing feels safer even when it is not.

How it works

Ritov and Baron (1990) asked parents to imagine a vaccine against a disease that kills ten children in ten thousand; if the vaccine itself could kill, most refused it unless its death rate was far below the disease's. The same asymmetry appeared with hypothetical drugs and investments (Spranca, Minsk and Baron, 1991): a harm you cause by acting feels like yours, a harm you allow feels like fate. Several things feed the bias. Actions are salient and easily blamed; omissions leave no causal trail; and moral rules are mostly phrased as prohibitions on doing rather than duties to prevent. Philosophers dispute whether the act-omission distinction is always an error, and in some domains people show the opposite “action bias” — goalkeepers dive on penalties although staying put would stop more (Bar-Eli and colleagues, 2007). But the persuasive uses are clear. Anyone defending a status quo can present its ongoing harms as nobody's fault while presenting any change as a harm someone chose; regulators are punished for approving a bad drug and never for delaying a good one; and a manipulator who withholds rather than lies can tell himself, and you, that he never did anything.

Real-world examples

  • •Ritov and Baron (1990): parents deciding whether to vaccinate against a disease that killed ten in ten thousand would accept a vaccine only if its own death rate was far lower — a preference for the larger harm, provided it came from doing nothing.
  • •Asch and colleagues (1994) found that parents who had refused the pertussis vaccine for their children scored higher on omission bias in hypothetical scenarios than parents who vaccinated — the bias was measurable in a real health decision, not only on paper.
  • •The US Food and Drug Administration is criticized publicly when an approved drug turns out to be harmful and almost never when a beneficial drug is delayed; economists have called the second category the invisible graveyard, because its victims are statistical and its cause is an omission.
  • •In the US health-care debates of 2010 and 2017, each side counted the harms the other's action would cause — plans cancelled under the Affordable Care Act, coverage lost through its repeal — while the harms of leaving the existing arrangement in place were treated as nobody's decision.
  • •A partner who lets you believe something false by staying silent, rather than by lying, is using the bias on both of you: withholding feels less culpable to the withholder and is harder to name as deception for the person misled.

Ethical guidelines

Where the line is

Preferring caution when the consequences of acting are genuinely less predictable than the consequences of waiting is reasonable; the line is crossed when a persuader counts only the harms of action — or hides behind the fact that no lie was told — so that a larger, quieter harm from inaction is treated as no one's responsibility.

  • ●Compare the expected harm of acting and of not acting on the same scale; if you would not accept a harm from action, do not accept a larger one from inaction because it leaves no fingerprints.
  • ●Do not defend a status quo by presenting its ongoing costs as natural and any change's costs as chosen; both are chosen.
  • ●Withholding information that you know would change someone's decision is a form of deception even though no false statement is made.
  • ●When you design incentives for regulators, doctors, or managers, reward avoided harms from inaction as visibly as you punish harms from action.

How to defend against it

  • ►Rewrite the choice so that both options are actions — “I choose to leave things as they are and accept the outcome” — then compare outcomes.
  • ►Ask for both numbers: what happens if we act, and what happens if we do not? A pitch that gives only the harms of acting is using the bias.
  • ►When someone says “I never lied to you”, ask what they knew and chose not to say; silence with knowledge is a decision.
  • ►For your own decisions, imagine explaining the inaction to the person it harmed; if that is uncomfortable, the omission was not neutral.
  • ►Name the framing out loud in policy arguments: “you are counting the harms of change and not the harms of staying put.”

References

  1. Ritov, I., & Baron, J. (1990). Reluctance to vaccinate: Omission bias and ambiguity. Journal of Behavioral Decision Making, 3(4), 263-277 · link
    The founding vaccination scenarios showing preference for harms of omission.
  2. Spranca, M., Minsk, E., & Baron, J. (1991). Omission and commission in judgment and choice. Journal of Experimental Social Psychology, 27(1), 76-105
    Generalization of the bias beyond vaccines and the analysis of why omissions are judged less harshly.
  3. 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
    The field finding that parents who refused pertussis vaccination showed stronger omission bias.
  4. Bar-Eli, M., Azar, O. H., Ritov, I., Keidar-Levin, Y., & Schein, G. (2007). Action bias among elite soccer goalkeepers: The case of penalty kicks. Journal of Economic Psychology, 28(5), 606-621
    The caveat that an opposite action bias appears in some contexts.
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