People's greater willingness to help identified victims, relative to non-identified ones, was examined by varying the singularity of the victim (single vs. a group of eight individuals), and the availability of individually identifying information (the main difference being the inclusion of a picture in the ''identified'' versions). Results support the proposal that the ''identified victim'' effect is largely restricted to situations with a single victim: the identified single victim elicited considerably more contributions than the non-identified single victim, while the identification of the individual group members had essentially no effect on willingness to contribute. Participants also report experiencing distress when the victim is single and identified more than in any other condition. Hence, the emotional reaction to the victims appears to be a major source of the effect.

In this article the authors develop a descriptive theory of choice using anticipated emotions. People are assumed to anticipate how they will feel about the outcomes of decisions and use their predictions to guide choice. The authors measure the pleasure associated with monetary outcomes of gambles and offer an account of judged pleasure called decision affect theory. Then they propose a theory of choices between gambles based on anticipated pleasure. People are assumed to choose the option with greater subjective expected pleasure. Similarities and differences between subjective expected pleasure theory and subjective expected utility theory are discussed. Emotions have powerful effects on choice. Our actual feelings of happiness, sadness, and anger both color and shape our decisions. In addition, our imagined feelings of guilt, elation, or regret influence our decisions. In this article we refer to these two influences as experienced emotions and anticipated emotions. Experienced emotions affect many levels of cognitive processing.

How do people feel about the outcomes of risky options? Results from two experiments demonstrate that the emotional reaction to a monetary outcome is not a simple function of the utility of that outcome Emotional responses also depend on probabilities and unobtained outcomes Unexpected outcomes have greater emotional impact than expected outcomes Furthermore any given outcome is less pleasant if an unobtained outcome is better We propose an account of emotional experiences associated with outcomes of decisions called decision affect theory It incorporates utilities expectations and counterfactual comparisons into hedonic responses Finally we show that choices between risky options can be described as the maximization of expected emotional experiences as predicted by decision affect theory That is people choose the risky option for which they expect to feel better on average

Subjects are reluctant to vaccinate a (hypothetical) child when the vaccination itself can cause death, even when this is much less likely than death from the disease prevented. This effect is even greater when there is a 'risk group' for death (with its overall probability held constant), even though the test for membership in the risk group is unavailable. This effect cannot be explained in terms of a tendency to assume that the child is in the risk group. A risk group for death from the disease has no effect on reluctance to vaccinate. The reluctance is an example of omission bias (Spranca, Minsk &Baron, in press), an overgeneralization of a distinction between commissions and omissions to a case in which it is irrelevant. Likewise, it would ordinarily be prudent to find out whether a child is in a risk group before acting, but in this case it is impossible, so knowledge of the existence of the risk group is irrelevant. The risk-group effect is consistent with Frisch & Baron's (1988) interpretation of ambiguity. KEY WORDS Omission bias Ambiguity VaccinationThe present study concerns the role of two biases in hypothetical decisions about vaccinations. One bias is the tendency to favor omissions over commissions, especially when either one might cause harm. We show that some people think that it is worse to vaccinate a child when the vaccination can cause harm than not to vaccinate, even though vaccination reduces the risk of harm overall. The other bias is the tendency to withhold action when missing information about probabilities is salientsuch as whether the child is in a risk group susceptible to harm from the vaccineeven though the missing information cannot be obtained. We show that this bias is found even when the overall probability of each outcome is clearly constant across the conditions compared. We take both of these effects to be overgeneralizations of principles or heuristics that are generally useful to situations in which they are not useful.Consider first what we shall call omission bias, the tendency to favor omissions (such as letting someone die) over otherwise equivalent commissions (such as killing someone actively). In most cases, we have good reasons for the distinction between omissions and commissions: omissions may result from ignorance, and commissions usually do not; commissions usually involve more malicious intentions than the corresponding omissions; and commissions usually involve more effort, itself a sign of stronger intentions. In addition, when people know that harmful omissions are socially acceptable, they look out for themselves; this self-help principle is, arguably, sometimes the most efficient way to prevent harm.

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