The heart of prospect theory is the value function, proposing that the carriers of value are positive or negative changes from a reference point. Daniel Kahneman observed that if prospect theory had a flag, the value function would be drawn on it. The function is nonlinear, reflecting diminishing sensitivity to magnitude. When describing how human lives are valued, the function exposes profound incoherence. An individual life is highly valued and thus vigorously protected if it is the only life at risk. But that life loses its value when it is one of many endangered by a larger tragedy. Beyond this insensitivity, the function may actually decline when many lives at risk become mere numbers. The more who die, the less we care. Implications of this deadly ‘arithmetic of compassion’ for understanding and managing the risk from nuclear weapons are briefly discussed.

People often choose the option that is better on the most subjectively prominentattribute — the prominence effect. We studied the effect of prominence inhealth care priority setting and hypothesized that values related to healthwould trump values related to costs in treatment choices, even when individualsthemselves evaluated different treatment options as equally good. We conductedpre-registered experiments with a diverse Swedish sample and a sample ofinternational experts on priority setting in health care (n = 1348).Participants, acting in the role of policy makers, revealed their valuation fordifferent medical treatments in hypothetical scenarios. Participants weresystematically inconsistent between preferences expressed through evaluation ina matching task and preferences expressed through choice. In line with ourhypothesis, a large proportion of participants (General population: 92%, Experts84% of all choices) chose treatment options that were better on the healthdimension (lower health risk) despite having previously expressed indifferencebetween those options and others that were better on the cost dimension. Thus,we find strong evidence of a prominence effect in health-care priority setting.Our findings provide a psychological explanation for why opportunity costs(i.e., the value of choices not exercised) are neglected in health care prioritysetting.

We employed simple gambles to investigate information processing in relation to the compatibility effect. Subjects should be more likely to engage in a deliberative thinking strategy when completing a pricing task rather than a rating task. We used eye-tracking methodology to measure information acquisition and processing in order to test the above hypothesis as well as to show that losses and alternatives with uncertain outcomes are more likely than gains and alternatives with sure outcomes to be processed through a deliberative thinking process. Results showed that pupil dilations, fixation duration and number of fixations increased when subjects evaluated the gambles with a pricing task. Additionally, the number of fixations increased as the gamble outcome became increasingly negative and when the outcome was uncertain (vs. sure). Fixations were also predictive of subjects’ final evaluations of the gambles. We discuss our results in light of the cognitive processes underlying different response modes in economic preferences.

Measuring reaction times to number comparisons is thought to reveal a processing stage in elementary numerical cognition linked to internal, imprecise representations of number magnitudes. These intuitive representations of the mental number line have been demonstrated across species and human development but have been little explored in decision making. This paper develops and tests hypotheses about the influence of such evolutionarily ancient, intuitive numbers on human decisions. We demonstrate that individuals with more precise mental-number-line representations are higher in numeracy (number skills) consistent with previous research with children. Individuals with more precise representations (compared to those with less precise representations) also were more likely to choose larger, later amounts over smaller, immediate amounts, particularly with a larger proportional difference between the two monetary outcomes. In addition, they were more likely to choose an option with a larger proportional but smaller absolute difference compared to those with less precise representations. These results are consistent with intuitive number representations underlying: a) perceived differences between numbers, b) the extent to which proportional differences are weighed in decisions, and, ultimately, c) the valuation of decision options. Human decision processes involving numbers important to health and financial matters may be rooted in elementary, biological processes shared with other species.

We present evidence from a pre-registered experiment indicating that a philosophical argument – a type of rational appeal – can persuade people to make charitable donations. The rational appeal we used follows Singer’s “shallow pond” argument (1972), while incorporating an evolutionary debunking argument (Paxton, Ungar and Greene, 2012) against favoring nearby victims over distant ones. The effectiveness of this rational appeal did not differ significantly from that of a well-tested emotional appeal involving an image of a single child in need (Small, Loewenstein and Slovic, 2007). This is a surprising result, given evidence that emotions are the primary drivers of moral action, a view that has been very influential in the work of development organizations. We found no support for our hypothesis that combining our rational and emotional appeals would have a stronger effect than either appeal in isolation. However, our finding that both kinds of appeal can increase charitable donations is cause for optimism, especially concerning the potential efficacy of well-designed rational appeals. We consider the significance of these findings for moral psychology, ethics, and the work of organizations aiming to alleviate severe poverty.

Donation requests often convey numerical information about the people in need. In two studies we investigated the effects of numeracy and presentation format on the underlying affective and cognitive mechanisms of donation decisions. In Study 1, participants were presented with information about a victim in need, either in a frequency format or in a percentage format. In Study 2, we manipulated the identifiability and number of target victims. Our results demonstrate that donations of individuals lower in numeracy were more susceptible to changes in numeric presentation format than those higher in numeracy. Importantly, the underlying mechanisms for donations differed by numeracy. Whereas the mental image of the victim influenced donation decisions of less numerate people only, the estimated impact of a donation was positively correlated with donation amounts for both more and less numerate individuals.

Empathic responses, such as sympathy towards others, are a key ingredient in the decision to provide help to those in need.The determinants of empathic responses are usually thought to be the vividness, similarity, and proximity of the victim. However, recent research highlights the role that attention plays in the generation of feelings. We expanded on this idea by investigating whether sympathy depends on cognitive mechanisms such as attention. In two studies we found that sympathy responses were lower and reaction times were longer when targets were presented with distractors. In addition, online sympathy judgments that allow attentional focusing on a target lead to greater affective responses than judgments made from memory. We conclude that attention is an ingredient in the generation of sympathy, and discuss implications for research on prosocial behaviour and the interaction between attention and emotions.

Three experiments demonstrate how the processing of negations is contingent on the evaluation context in which the negative information is presented. In addition, the strategy used to process the negations induced different affective reactions toward the stimuli, leading to inconsistency of preference. Participants were presented with stimuli described by either stating the presence of positive features (explicitly positive alternative) or negating the presence of negative features (non-negative alternative). Alternatives were presented for either joint (JE) or separate evaluation (SE). Experiment 1 showed that the non-negative stimuli were judged less attractive than the positive ones in JE but not in SE. Experiment 2 revealed that the non-negative stimuli induced a less clear and less positive feeling when they were paired with explicitly positive stimuli rather than evaluated separately. Non-negative options were also found less easy to judge than the positive ones in JE but not in SE. Finally, Experiment 3 showed that people process negations using two different models depending on the evaluation mode. Through a memory task, we found that in JE people process the non-negative attributes as negations of negative features, whereas in SE they directly process the non-negative attributes as positive features.

There is an increased willingness to help identified individuals rather than non-identified, and the effect of identifiability is mainly present when a single individual rather than a group is presented. However, identifiability and singularity effects have thus far not been manipulated orthogonally. The present research uses a joint evaluation approach to examine the relative contribution of identifiability and singularity in moral decision-making reflecting conflicting values between deontology and consequentialism. As in trolley dilemmas subjects could either choose to stay with the default option, i.e., giving a potentially life-saving vaccine to a single child, or to actively choose to deny the single child the vaccine in favor of five other children. Identifiability of the single child and the group of children was varied between-subjects in a 2x2 factorial design. In total 1,232 subjects from Sweden and the United States participated in three separate experiments. Across all treatments, in all three experiments, 32.6% of the subjects chose to stay with the deontological default option instead of actively choosing to maximize benefits. Results show that identifiability does not always have a positive effect on decisions in allocation dilemmas. For single targets, identifiability had a negative or no effect in two out of three experiments, while for the group of targets identifiability had a more stable positive effect on subjects’ willingness to allocate vaccines. When the effect of identifiability was negative, process data showed that this effect was mediated by emotional reactance. Hence, the results show that the influence of identifiability is more complex than it has been previously portrayed in the literature on charitable giving.

This paper asks whether moral preferences in eight medical dilemmas change as a function of how preferences are expressed, and how people choose when they are faced with two equally attractive help projects. In two large-scale studies, participants first read dilemmas where they “matched” two suggested helping projects (which varied on a single attribute) so that they became equally attractive. They did this by filling in a missing number (e.g., how many male patients must Project M save in order to be equally attractive as Project F which can save 100 female patients). Later, the same participants were asked to choose between the two equally attractive projects. We found robust evidence that people do not choose randomly, but instead tend to choose projects that help female (vs. male), children (vs. adult), innocent (vs. non-innocent), ingroup (vs. outgroup) and existing (vs. future) patients, and imply no (vs. some) risk of a harmful side-effect, even when these projects have been matched as equally attractive as, and save fewer patients than the contrasting project. We also found that some moral preferences are hidden when expressed with matching but apparent when expressed with forced choice. For example, 88–95% of the participants expressed that female and male patients are equally valuable when doing the matching task, but over 80% of them helped female patients in the choice task.

There is a worldwide and increasing shortage of potable fresh water. Modern water reclamation technologies can alleviate much of the problem by converting wastewater directly into drinking water, but there is public resistance to these approaches that has its basis largely in psychology. A psychological problem is encapsulated in the saying of those opposing recycled water: “toilet to tap.” We report the results of two surveys, one on a sample of over 2,000 Americans from five metropolitan areas and the second on a smaller sample of American undergraduates, both assessing attitudes to water and water purification. Approximately 13% of our adult American sample definitely refuses to try recycled water, while 49% are willing to try it, with 38% uncertain. Both disgust and contamination sensitivity predict resistance to consumption of recycled water. For a minority of individuals, no overt treatment of wastewater will make it acceptable for drinking (“spiritual contagion”), even if the resultant water is purer than drinking or bottled water. Tap water is reliably rated as significantly more desirable than wastewater that has undergone substantially greater purification than occurs with normal tap water. Framing and contagion are two basic psychological processes that influence recycled water rejection.

Environmental events such as natural disasters may influence the public's affective reactions and decisions. Shortly after the 2004 Tsunami disaster we assessed how affect elicited by thinking about this disaster influenced risk perceptions and future time perspective in Swedish undergraduates not directly affected by the disaster. An experimental manipulation was used to increase the salience of affect associated with the disaster. In Study 1 we found that participants reminded about the tsunami had a sense that their life was more finite and included fewer opportunities than participants in the control condition (not reminded about the tsunami). In Study 2 we found similar effects for risk perceptions. In addition, we showed that manipulations of ease-of-thought influenced the extent to which affect influenced these risk perceptions, with greater ease of thoughts being associated with greater perceived risks.

Subjects who judged speed in a driving scenario overestimated how fast they could decelerate when speeding compared to when keeping within the speed limit (Svenson, 2009). The purpose of the present studies were to replicate studies conducted in Europe with subjects in the U.S., to study the influence of speed unit (kph vs. mph), affective reactions to outcome (collision) and identity of main actor (driver) on braking speed judgments. The results replicated the European findings and the outcome affective factor (passing a line/killing a child) and the actor factor (subject/driver in general) had significant effects on judgments of braking speed. The results were related to psychological theory and applied implications were discussed.

Compassion shown towards victims often decreases as the number of individuals in need of aid increases, identifiability of the victims decreases, and the proportion of victims helped shrinks. Such “compassion fade” may hamper individual-level and collective responses to pressing large-scale crises. To date, research on compassion fade has focused on humanitarian challenges; thus, it remains unknown whether and to what extent compassion fade emerges when victims are non-human others. Here we show that compassion fade occurs in the environmental domain, but only among non-environmentalists. These findings suggest that compassion fade may challenge our collective ability and willingness to confront the major environmental problems we face, including climate change. The observed moderation effect of environmental identity further indicates that compassion fade may present a significant psychological barrier to building broad public support for addressing these problems. Our results highlight the importance of bringing findings from the field of judgment and decision making to bear on pressing societal issues.

Recent research on charitable donations shows that donors evaluate both the impact of helping and its cost. We asked whether these evaluations were affected by the context of alternative charitable causes. We found that presenting two donation appeals in joint evaluation, as compared to separate evaluation, increased the perceived benefit of the cause ranked as more important (Study 1), and decreased its perceived cost, regardless of the relative actual costs (Study 2). Finally, we try to reconcile an explanation based on perceived cost and benefit with previous work on charitable donations.

Most people are caring and will exert great effort to rescue individual victims whose needy plight comes to their attention. These same good people, however, often become numbly indifferent to the plight of individuals who are “one of many” in a much greater problem. Why does this occur? The answer to this question will help us answer a related question that is the topic of this paper: Why, over the past century, have good people repeatedly ignored mass murder and genocide? Every episode of mass murder is unique and raises unique obstacles to intervention. But the repetitiveness of such atrocities, ignored by powerful people and nations, and by the general public, calls for explanations that may reflect some fundamental deficiency in our humanity — a deficiency that, once identified, might possibly be overcome. One fundamental mechanism that may play a role in many, if not all, episodes of mass-murder neglect involves the capacity to experience affect, the positive and negative feelings that combine with reasoned analysis to guide our judgments, decisions, and actions. I shall draw from psychological research to show how the statistics of mass murder or genocide, no matter how large the numbers, fail to convey the true meaning of such atrocities. The reported numbers of deaths represent dry statistics, “human beings with the tears dried off,” that fail to spark emotion or feeling and thus fail to motivate action. Recognizing that we cannot rely only upon our moral feelings to motivate proper action against genocide, we must look to moral argument and international law. The 1948 Genocide Convention was supposed to meet this need, but it has not been effective. It is time to examine this failure in light of the psychological deficiencies described here and design legal and institutional mechanisms that will enforce proper response to genocide and other forms of mass murder.

Why does public conflict over societal risks persist in the face of compelling and widely accessible scientific evidence? We conducted an experiment to probe two alternative answers: the ‘science comprehension thesis’ (SCT), which identifies defects in the public's knowledge and reasoning capacities as the source of such controversies; and the ‘identity-protective cognition thesis’ (ICT), which treats cultural conflict as disabling the faculties that members of the public use to make sense of decision-relevant science. In our experiment, we presented subjects with a difficult problem that turned on their ability to draw valid causal inferences from empirical data. As expected, subjects highest in numeracy – a measure of the ability and disposition to make use of quantitative information – did substantially better than less numerate ones when the data were presented as results from a study of a new skin rash treatment. Also as expected, subjects’ responses became politically polarized – and even less accurate – when the same data were presented as results from the study of a gun control ban. But contrary to the prediction of SCT, such polarization did not abate among subjects highest in numeracy; instead, it increased. This outcome supported ICT, which predicted that more numerate subjects would use their quantitative-reasoning capacity selectively to conform their interpretation of the data to the result most consistent with their political outlooks. We discuss the theoretical and practical significance of these findings.