The self-discovery of a suspicious symptom often brings about an emotional turbulence: while recognizing the importance of having the symptom diagnosed promptly, individuals frequently delay diagnosis, seeking to avoid the pain or discomfort associated with the diagnostic process and fearing to hear that they are developing a serious illness. The present paper proposes a rational, economic-oriented approach to explaining individuals' delay behavior, weighing the fear of the diagnostic procedure and of being told the suspected truth against the fear of consequence of further procrastination. Assuming that the money costs of diagnosis and medical treatment are borne by health insurance, a multi-period expected-utility maximization model is constructed to inquire into the individual's decision of whether and to what extent to delay diagnosis. The results rationalize a variety of observed behavior concerning individuals' reaction to suspicious symptoms that differ in their psychic cost of diagnosis, the likelihood of indicating severe illness and the potential damage to health incurred by delayed diagnosis. The desirability of delayed diagnosis to the health insurer and the socially desired solution are finally discussed.

Utility theory as developed by Von Neuman and Morgenstern provides an elegant way to make consistent choices among risky alternatives by maximizing the expected value of a personal utility function over known probability distributions of outcomes. The theory is usually presented in the context of a single (possibly complex) decision, where it gives little guidance on the choice of a utility function. This paper provides a tutorial on the consequences of applying expected utility theory to repeated decisions, using theory and simulation to reveal the statistical regularity arising cumulatively from repeatedly applying the same utility. If decisions are repeated and consequences accumulate, two utility functions stand out as maximizing cumulative incremental growth and cumulative compound growth, namely the linear utility and the logarithmic utility, respectively. Repeatedly basing decisions on the linear utility when compound growth applies and severe losses are possible can be disastrous in the long term. Relevance to financial investment and population catastrophes is considered.

The standard account of the ‘reflection effect’ (Kahneman and Tversky, 1979) is that attitude toward risk changes across gain or loss framings of outcomes. Weber and Bottom (1989) proposed an alternative account in which decision makers have stable risk attitudes, but changing risk perceptions. Undergraduates were randomly assigned to read one of three hypothetical informed consent documents from a trial of a cholesterol-lowering drug. Documents used gain, loss or both framings to describe expected benefits. Respondents rated riskiness of participation and non-participation in the trial and made a choice about whether they would participate in the trial.

The reflection effect was replicated. In addition, as predicted by the Weber and Bottom account, respondents in the gain condition were more likely to rate participation as riskier than non-participation compared to respondents in the loss condition, and in each condition more than 70 per cent of respondents chose to avoid the option they judged as riskier. Implications for informed consent are discussed.

This paper describes the HARIA-2 methodology for external emergency planning and analysis. The main aim of the HARIA-2 research project is to investigate the possibility of taking into account not only the physical phenomena, but also sociological aspects in technological emergencies. The methodology has been implemented in two software packages.

1. DEMONSTRATOR, which allows to efficiently simulate various accident scenarios; it can also be used for training rescue services and as a support tool for decision making during real emergencies;

2. PROTOTYPE system, addressing emergency planning issues, developed on a commercial GIS platform (Arc-View 3.2©); it integrates all data bases and models developed, including those simulating population behaviour and the evacuation plan, even though in a simplified mode.

The paper describes the main aspects of the HARIA-2 methodology and two examples of application, namely the Mexico City disaster (1984) and a simulation exercise of evacuation for the Milazzo industrial area.

When people attempt to evaluate their personal standing on a variety of dimensions, they often compare themselves with others. This assertion was central to the development of social comparison theory (Festinger, 1954), and has stimulated nearly 50 years of research – primarily in the areas of social psychology, clinical psychology, organizational behavior, and sociology. Social comparison processes have been explored in a broad range of domains including coping, negotiation, academic and work performance, happiness, emotion, and motivation. Numerous volumes have appeared on extensions and applications of the theory, including a recent handbook edited by Suls and Wheeler (2000).

Klein (1997) found that participants were more influenced by information about their comparative risk standing than information about their absolute risk standing. If reliable, these findings have important implications for understanding and improving risk communication. In this paper we report the findings of several unsuccessful attempts by us to replicate Klein's findings in the UK, using one of his experimental paradigms, and discuss the findings of other recent attempts to replicate his work. Findings are inconsistent from study to study but, overall, provide some evidence that people respond to comparative and not just to absolute risk information. Issues that need to be addressed systematically in future research include: the ambiguity of absolute information, proportional differences in risk magnitude, cross-cultural and individual differences in preferences for social comparison information, and the systematic exploration of responses to absolute and comparative risk information in real choice situations.

Using an experimental manipulation embedded in a national survey, this study investigated the effect on smokers' risk judgments of receiving accurate information about the cigarette consumption of the average smoker. It was hypothesized that this information would reduce smokers' estimates of the risk of lung cancer faced by the average smoker (‘other's risk’) and hence influence their comparative risk judgments. As predicted, the information made lighter smokers more optimistic and heavier smokers less optimistic. However, the experimental manipulation had no effect on intention to give up smoking. The difference score (other's risk minus own risk) correlated 0.52 with the single-item comparative risk measure. The former measure showed a small but significant optimistic bias whereas the latter measure showed a small but significant pessimistic bias. The findings are discussed in terms of measurement issues and the implications for interventions designed to influence risk perceptions.

The current study examined the hypothesis that adolescents' absolute and comparative perceptions of vulnerability to potential negative consequences of substance use mediate the relation between traditional predictors of use, and actual substance use. The data support the hypothesis in that absolute risk perceptions mediate the relations between parental communication about substances, peer substance use and risk-taking tendency, and subsequent adolescent use. Comparative risk perceptions, however, are only weakly related to these three predictors, and do not predict subsequent use. The data also replicate earlier findings that behavioral willingness mediates the relation between risk perceptions and behavior. Methodological and applied implications are discussed.

This study explored whether comparisons of one's perceived absolute risk of being overweight to that of other people are predictive of concern about one's risk and intentions to reduce it. One hundred and six North American college students rated their absolute risk, concern, and intentions, and compared their risk with that of several comparison referents including average targets (e.g., ‘the average same-sex student in the US’), single targets (e.g., ‘best friend’), temporal targets (e.g., ‘yourself a few years ago’), and exemplar targets (e.g., ‘prototypical person with weight problem’). Participants showed high concern and intentions when comparing unfavorably with many of the average targets, even when controlling for absolute risk. Comparisons with single targets were generally related to concern, though not to intentions. Temporal and exemplar comparisons were unrelated to concern and intentions. Comparative risk (particularly with average targets) may elicit worry about one's risk and encourage protective measures, irrespective of one's absolute risk.

In a nationwide study, we explored how Israelis, currently stricken by an intense wave of terrorism, perceive the risk of being the victim of a terrorist attack. We studied both absolute and comparative (i.e., vis-a-vis other people at the area of residence) perceived controllability and vulnerability. The picture that emerges is one of realism. We found no evidence of the comparative optimistic illusions, which characterizes the risk-perception literature. Most participants report some level of behavior change and precautions against the threat of terrorism, but most of them were doubtful about the effectiveness of these precautionary attempts. Perceived absolute vulnerability was the only risk perception variable related to precautionary behaviors. We discuss the disappearance of comparative optimistic biases when the threat is clearly realistic.