Omission bias

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The Omission Bias is a type of cognitive bias. It is the tendency to judge harmful actions as worse, or less moral than equally harmful omissions (inactions.) When it comes to making a decision, this bias is similar to the Status quo bias, because they both favor the default, which in the case of the Omission Bias is not acting.

Omission Bias applies very much to vaccination. There have been many recorded incidents where parents do not inoculate small children because of the risk associated with the vaccination itself. They feel that if a child is exposed to the risk of death from vaccination, they should not act and retain the default. This is a bias, because the parent is clearly making the erroneous decision by exposing the child to a higher risk of death by not vaccinating. If the risk of death from the vaccination itself is smaller than the risk the child would face if not vaccinated, then clearly the optimal choice according to Expected Utility Theory would be to vaccinate. The source of the risk is irrelevant.

Spranca, Minsk and Baron extended the Omission Bias to judgments of morality of choices. In one scenario, John, a tennis player, would be facing a tough opponent the next day in a decisive match. John knows his opponent is allergic to a food substance. Subjects were presented with two conditions: John recommends the food containing the allergen to hurt his opponent’s performance, or the opponent himself orders the allergenic food, and John says nothing. A majority of people judged that John’s action of recommending the allergenic food as being more immoral than John’s inaction of not informing the opponent of the allergenic substance.