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Psychology of Patient Sections
Author Bio
Introduction
Currently selected section: Omission Bias
Discount Rates
Framing
Assessing Probabilities
Predicting Utility
Sequences
Role-based decisions
Role of Emotions
Visceral Influences
Conclusion
Chapter 4: The Psychology of Patient Decision Making: The Omission Bias
        

The omission bias is manifested when a more harmful act of omission is preferred to a less harmful act of commission.  To illustrate this point, consider this question taken from Asch et al., (1994).  After reading the question, please choose an answer.

Imagine that, in the state in which you live in, there had been several epidemics of a certain kind of flu which can be fatal to children under 3.  A vaccine for this kind of flu has been developed and tested.  The vaccine eliminates the chance of getting the flu.  The vaccine, however, might cause side effects that are also sometimes fatal. Out of every 10,000 children under 3 who are not vaccinated, 10 will die from the flu.

Suppose that the overall death rate for vaccinated children were 5 out of 10,000.  Would you vaccinate your child?  (Choose one of the two options.)

       

This seems like an easy question to answer, because the vaccination is much less lethal than the disease it prevents.  However, if you would permit vaccination of your child under these circumstances, you would not agree with the majority of the parents who responded to the survey by Asch et al.  Most parents responding to this survey preferred to omit the vaccination when it caused 5 deaths per 10,000, thereby exposing their children to a higher mortality rate from the disease!  This finding represents an example of the omission bias, because the more harmful act of omitting the vaccination is preferred to a less harmful act of vaccinating.

Asch et al. related parents’ responses to the survey to the parents’ actual decisions to have their children vaccinated with diphtheria-pertussis-tetanus vaccine (DPT).  This vaccine does have rare, serious side effects.  Those parents who either did permit their children to be given DPT vaccine or intended to do so were willing to tolerate a risk of 5.4 deaths from the flu vaccine in the above hypothetical scenario.  Those who would not allow their children to be given DPT vaccine required that the flu vaccine in the scenario cause no more than 2.4 deaths.  The parents who would not permit DPT vaccinations indicated that they would “ . . . feel responsible if anything had happened because of DPT vaccine.”  They tended not to endorse the notion that they would “ . . . feel responsible if anything had happened because I failed to vaccinate.”  In other words, many parents feel more responsible for a bad outcome if it takes place following their action than if the bad outcome simply occurs, even if their action would have made the bad outcome far less likely.  This is the hallmark of the omission bias.


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