Omission Bias

What it is

In ordinary decisions, leaving things alone is both a way of keeping the status quo and a way of not acting, so the two tendencies cannot be told apart. Ritov and Baron built scenarios in which change happens unless someone acts. In those scenarios doing nothing no longer preserves the current state, and the question becomes which of the two preferences a person follows.

In effect

Participants reacted more strongly to bad outcomes caused by action, whether or not the action preserved the status quo. They chose inaction even when inaction still led to change. A matching task that required no action showed no status quo bias. The authors concluded that the status quo bias is at least partly driven by a bias toward omission.

Where the term comes from

Spranca, Minsk and Baron (1991) gave subjects scenarios about pairs of options, one an omission and one a commission, with intentions, motives and consequences held constant. Subjects often rated harmful omissions as less immoral, or less bad as decisions, than harmful commissions, and those ratings went with judgments that omissions do not cause outcomes. The authors found no matching effect for good outcomes, so the pattern is not simply an exaggerated response to commissions, and a few subjects were even willing to accept greater harm to avoid acting. They describe the omission bias as an overgeneralisation of a useful heuristic to cases where it is not justified. Further experiments indicated that judgments depend on features that ordinarily distinguish omissions from commissions: physical movement in commissions, the presence of salient alternative causes in omissions, and the fact that the consequences of omissions would occur anyway.

Ritov and Baron (1990) carried the idea into health decisions. Subjects were reluctant to vaccinate a hypothetical child when the vaccine itself can cause death, even when that is much less likely than death from the disease it prevents, and the reluctance grew when a risk group for death was introduced with the overall probability held constant. Their abstract cites Spranca, Minsk and Baron, then in press, for the term.

What it does not say

The finding does not remove status quo bias; it says part of it is something else. Other accounts attribute the bias to loss aversion, as Daniel Kahneman does in Thinking, Fast and Slow, or to a general preference for the status quo, as David Gal argued in 2006.

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