Emotions play at least two major roles in decision making.  First, one’s current emotions can distort the decision making process.  For example, when one is in a bad mood, one is more likely to recall negative events (Bower, 1981) and overestimate the likelihood of unfortunate occurrences (Johnson and Tversky, 1983).  When one is in a good mood, we are more likely to remember positive events (Bower, 1982) and be more optimistic about their future occurrence (Wright and Bower, 1992).  The implication of these findings is that if one solicits recollection or probability estimates from a patient, the patient’s response is likely to be distorted by the current emotional state.

A second major role of emotions in decision making is that our choice of options is influenced by the anticipated emotion we think we would feel if we chose each option.  For example, if I find an item I want at a very good price, should I buy it?  I might not if I think that I might find it a better price later today.  If I buy it now and see it at a better price later, my regret may be so troubling that I would prefer not to have made the initial purchase.

To illustrate the role of anticipated emotions in a medical situation, consider another vaccination scenario, this one taken from Ritov and Baron (1995, p. 125).

A type of flu can be fatal to young children. A vaccine can prevent the flu...However, the vaccine can also be fatal. Children who die from the vaccine would not necessarily have died anyway from the flu.  Ten out of every 10,000 children will die from the flu if they are not vaccinated.  You are a public health official in a foreign county, and you must decide whether to vaccinate the children in your district.  You plan to leave soon, so you will not see the individual children after you make your decision.

You will never know what happened to any of the children, and you will never know what would have happened if you had decided differently.

Would you want to vaccinate your patients if the death rate from the vaccine were each of the following? 

0 out of 10,000

3 out of 10,000

5 out of 10,000

7 out of 10,000

11 out of 10,000

Now re-consider the scenario with a small change.  Rather than reading that you will never know anything about the fate of the children, you read the following:

"After you leave, you will see reports about each child in your district.  You will know which children died from the flu, if any, and which died from the vaccine, if any.  Also, you will see, for each child, the results of a test to determine which vaccinated children would have died from the flu and which unvaccinated children would have died from the vaccine. So you will know, for each child, both what happened and what would have happened had you decided differently.”

Would this modification in the scenario cause you to change the number of deaths you would tolerate as you decide whether or not to vaccinate the children?  Should it?

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