The Use of Narrative Evidence and Explicit Likelihood by Decisionmakers Varying in Numeracy

Decisionmakers are often presented with explicit likelihood assessments (e.g., there is a 10% chance that an attack will occur over the next three months) and supporting narrative evidence in forecasting and risk communication domains. Decisionmakers are thought to rely on both numerical and narrative information to the extent that they perceive the information to be diagnostic, accurate, and trustworthy. In two studies, we explored how lay decisionmakers varying in numeracy evaluated and used likelihood assessments and narrative evidence in forecasts. Overall, the less numerate reported higher risk and likelihood perceptions. In simple probabilistic forecasts without narrative evidence, decisionmakers at all levels of numeracy were able to use the stated likelihood information, although risk perceptions of the less numerate were more affected by likelihood format. When a forecast includes narrative evidence, decisionmakers were better able to use stated likelihood in a percentage as compared to frequency or verbal formats. The more numerate used stated likelihood more in their evaluations whereas the less numerate focused more on the narrative evidence. These results have important implications for risk analysts and forecasters who need to report the results of their analyses to decisionmakers. Decisionmakers varying in numerical ability may evaluate forecasts in different ways depending on the types of information they find easiest to evaluate.     

Why Study Risk Perception?

Studies of risk perception examine the opinions people express when they are asked, in various ways, to characterize and evaluate hazardous activities and technologies. This research aims to aid risk analysis and societal decision making by (i) improving methods for eliciting opinions about risk, (ii) providing a basis for understanding and anticipating public responses to hazards, and (iii) improving the communication of risk information among laypeople, technical experts, and policy makers.     

Lay Understanding of Synergistic Risk: The Case of Radon and Cigarette Smoking

The combination of radon and smoking produces a synergistic risk of lung cancer. Lay understanding of this risk was examined from the perspectives of mental models theory, the psychometric approach to risk perception, and optimistic bias. As assessed by interview, participants ( N = 50) had more extensive mental models for the risks of smoking than for the risks of radon or the combination of radon and smoking; 32% knew little or nothing about radon. Despite reading an informational brochure, their risk-perception ratings of the three hazards showed no perception of the synergy between smoking and radon risk, although the combined hazard was rated as less familiar but more controllable than the average of the single hazards ( p < .01). No evidence of optimistic bias for the health consequences of radon, or the combination of radon and smoking was observed. Participants appeared to be combining the single-hazard risks subadditively to arrive at their combined-hazard risk perceptions. Further research on the integration of perceived risks would be beneficial for designing optimal communications about synergistic risk.     

Effect of Risk Ladder Format on Risk Perception in High- and Low-Numerate Individuals

Utilizing a random sample from the general population ( N = 257), we examined the effect of the radon risk ladder on risk perception, as qualified by respondents' numeracy. The radon risk ladder provides comparative risk information about the radon equivalent of smoking risk. We compared a risk ladder providing smoking risk information with a risk ladder not providing this information. A 2 (numeracy; high, low) × 3 (risk level; high, medium, low) × 2 (smoking risk comparison: with/without) between subjects experimental design was used. A significant ( p < 0.045) three-way interaction between format, risk level, and numeracy was identified. Participants with low numeracy skills, as well as participants with high numeracy skills, generally distinguished between low, medium, and high risk levels when the risk ladder with comparative smoking risk information was presented. When the risk ladder without the comparative information about the smoking risk was presented, low-numerate individuals differentiated between risk levels to a much lesser extent than high-numerate individuals did. These results provide empirical evidence that the risk ladder can be a useful tool in enabling people to interpret various risk levels. Additionally, these results allow us to conclude that providing comparative information within a risk ladder is particularly helpful to the understanding of different risk levels by people with low numeracy skills.     

Conventional Wisdom on Risk Communication and Evidence from a Field Experiment

A recent comprehensive review of the literature identified a number of facts and principles governing risk communication. This paper evaluates several of these propositions using recent evidence from a field experiment in communicating the risks from radon in homes. At this point in the research, data relates primarily to the response of risk perceptions to different information treatments and different personal characteristics. The effect of various causal factors is sensitive to the particular test of risk perception applied. No information treatment was clearly superior for all tasks. An important implication of these findings is that risk communicators must determine what specific task or tasks the information program should enable people to do.     

Agency Communication, Community Outrage, and Perception of Risk: Three Simulation Experiments

Three experimental studies were conducted employing hypothetical news stories to compare the effects on reader risk perceptions of two situations: when agency communication behavior was reported to be responsive to citizens' risk concerns, vs. when the agency was reported to be unresponsive. In the first two experiments, news stories of public meetings filled with distrust and controversy led to ratings indicating greater perceived risk than news stories reporting no distrust or controversy, even though the risk information was held constant. This effect appeared clearly when the differences in meeting tone were extreme and subjects made their ratings from their recall of the stories, but it was much weaker when the differences were moderate and subjects were allowed to go back over the news stories to help separate risk information from conflict information. In the third experiment, news stories about a spill cleanup systematically varied the seriousness of the spill, the amount of technical information provided in the story, and the agency behavior and resulting community outrage. The outrage manipulation significantly affected affective and cognitive components of perceived risk, but not hypothetical behavioral intentions. Seriousness and technical detail had very little effect on perceived risk.     

The Perceived Health Risks of Indoor Radon Gas and Overhead Powerlines: A Comparative Multilevel Approach

Radon and overhead powerlines are two radiation risk cases that have raised varying levels of concern among the general public and experts. Despite both involving radiation—a typically feared and unseen health hazard—individuals' perceptions of the two risk cases may invoke rather different factors. We examined individual and geographic-contextual factors influencing public perceptions of the health risks of indoor radon gas and overhead powerlines in a comparative research design, utilizing a postal questionnaire with 1,528 members of the general public (response rate 28%) and multilevel modeling techniques. This study found that beliefs about the two risk cases mainly differed according to the level of "exposure"—defined here in terms of spatial proximity. We argue that there are two alternative explanations for this pattern of findings: that risk perception itself varies directly with proximity, or that risk is more salient to concerned people in the exposed areas. We also found that while people living in high radon areas are more concerned about the risks of indoor radon gas, they find these risks more acceptable and have more trust in authorities. These results might reflect the positive effects of successive radon campaigns in high radon areas, which may have raised awareness and concern, and at the same time may have helped to increase trust by showing that the government takes the health risks of indoor radon gas seriously, suggesting that genuine risk communication initiatives may have positive impacts on trust in risk management institutions.     

Designing Risk Communications: Completing and Correcting Mental Models of Hazardous Processes, Part I

Many risk communications are intended to help the lay public make complex decisions about risk. To guide risk communicators with this objective, a mental models approach to the design and characterization of risk communications is proposed. Building on text comprehension and mental models research, this approach offers an integrated set of methods to help the risk communication designer choose and analyze risk communication content, structure, and organization. An applied example shows that two radon brochures designed with this approach present roughly the same expert facts as a radon brochure widely distributed by the U.S. EPA but meet higher standards on other content, structure, and organization criteria.     

Perception of Risk and Credibility at Toxic Sites

This study integrates previous research methodologies to compare the risk perceptions and responses to risk messages of agency personnel and neighbors of Superfund sites in Michigan. The integration attempted and the focus on risk messages are shaped by a critical review of the social amplification conceptual framework. The study involved all four agency groups and three groups of site neighbors actively involved in Superfund planning across the state. The first part of the study utilized the psychometric techniques of hazard rating and hazard profiles that had not previously been used in studies involving stakeholders. While agency personnel responded similarly to experts in previous studies, the responses of individuals in the neighbor groups reflected experience with toxic sites and were dissimilar to previous ratings by the general public. The second part of the study consisted of a hypothetical toxic site scenario that focused on specific risk messages at different times in the site history. Results indicate that the difference in perception of risk occurs after the first testing at a site, and that dramatic differences arise between agency and resident groups regarding the credibility of information sources and the need for independent testing. A general lack of trust in the Superfund program was demonstrated by all groups. The results indicate that problems of institutional credibility and program adequacy cannot be addressed by better risk communication.     

The Indoor Radiological Problem in Perspective

Measures to tighten homes to conserve energy, as are being encouraged and subsidized by federal and state governments, may reduce air infiltration by 20% or more. Standard prudent risk-assessment methodologies predict that, due to increased levels of indoor radon caused by this reduction in ventilation, the added lifetime lung cancer risk to members of the public is of order 200/million people exposed. In situations where the radon source term is unusually high, or extreme reductions in ventilation are made, the added risk can be more than an order of magnitude greater. While these imputed risks are far outside the range that is normally tolerated, no systematic efforts are in progress to mitigate or limit the risk in any way. Furthermore, efforts to determine better the variations in radon source term and the health effects of indoor radon are being deemphasized. The technical background is presented in some detail, and implications with regard to management of risks to the public are discussed.     

Probability Information in Risk Communication: A Review of the Research Literature

Communicating probability information about risks to the public is more difficult than might be expected. Many studies have examined this subject, so that their resulting recommendations are scattered over various publications, diverse research fields, and are about different presentation formats. An integration of empirical findings in one review would be useful therefore to describe the evidence base for communication about probability information and to present the recommendations that can be made so far. We categorized the studies in the following presentation formats: frequencies, percentages, base rates and proportions, absolute and relative risk reduction, cumulative probabilities, verbal probability information, numerical versus verbal probability information, graphs, and risk ladders. We suggest several recommendations for these formats. Based on the results of our review, we show that the effects of presentation format depend not only on the type of format, but also on the context in which the format is used. We therefore argue that the presentation format has the strongest effect when the receiver processes probability information heuristically instead of systematically. We conclude that future research and risk communication practitioners should not only concentrate on the presentation format of the probability information but also on the situation in which this message is presented, as this may predict how people process the information and how this may influence their interpretation of the risk.     

Awareness and Perceptions of the Risks of Exposure to Indoor Radon: A Population‐Based Approach to Evaluate a Radon Awareness and Testing Campaign in England and Wales

The current study aimed to evaluate the locally directed radon roll‐out program that was conducted between 2001 and 2005 in England and Wales to increase radon awareness and testing rates. A representative sample of 1,578 residents aged 16 and older were interviewed who lived in radon‐affected areas of 15 local authorities in England and Wales that were eligible for participation in the program. The study systematically sampled across participating and nonparticipating local authorities, “actionable” and “nonactionable” radon‐affected areas, and geographic regions with different campaign histories (Wales, Southwest England, and the rest of England). As a multistage sampling strategy was used, the data were analyzed from a multilevel perspective. This study found that participants living in participating local authorities had higher levels of awareness and were more likely to have tested their home for radon than participants living in nonparticipating local authorities. Similar results were found for participants living in “actionable” areas as compared to those living in “nonactionable” radon‐affected areas. The study further found that radon awareness and testing rates were the highest in Southwest England and the lowest in Wales. This study suggests that the radon roll‐out program has been effective in raising awareness and testing rates, and that ongoing domestic radon campaigns in Southwest England may have raised radon awareness and testing in these areas, showing important reinforcement effects of multiple risk communication campaigns.     

Helping Individuals to Understand Synergistic Risks: An Assessment of Message Contents Depicting Mechanistic and Probabilistic Concepts

Accumulating evidence shows that certain hazard combinations interact to present synergistic risks. However, little is known about the most effective ways of helping individuals to understand this complex risk concept. More specifically, there is an absence of empirical research that has assessed the relative efficacy of messages that explain either the causal mechanism and/or the probabilistic components of synergistic risks. In an experiment designed to address this issue, we presented participants with messages concerning the synergistic risk of developing esophageal cancer for individuals who consume both tobacco and alcohol. Relative to a control group, we compared the extent to which messages featuring content detailing the underlying biological mechanism, the probabilistic risk, or both improved understanding of the synergistic risk. Our results showed that messages containing details of both the mechanism and probabilistic information were most effective at enabling individuals to understand that the alcohol‐tobacco combination presents a synergistic risk. In addition, large improvements in the accuracy of cancer frequency estimates were observed amongst individuals who received probabilistic information, and the highest relative increase in professed willingness to adopt precautionary behaviors was observed amongst individuals who received the mechanism information only. Importantly, these findings could be utilized in the development of a general model for the communication of synergistic risks. Furthermore, in contrast to previous findings, our study demonstrates that risk messages can be both effective and efficient in helping individuals to acquire a greater understanding of synergistic risks. Acquiring such knowledge could lead to significant improvements in risk‐related decisions concerning combined hazards.     

The Risks of "Putting the Numbers in Context": A Cautionary Tale

Despite the warnings of risk communication specialists, members of the technical community often urge that technological risks should be "put in context" by comparisons against risks that are more familiar. Little quantitative evidence is available on the actual behavioral consequences of such risk comparison efforts. In the present study, subjects were presented with two types of information about a hazardous waste incinerator–a simplified statistical summary and a comparison of incinerator risks against the risks of smoking. Statistical information led to a modest increase in the reported willingness to vote in favor of the incinerator in a community referendum, but the comparison against cigarettes led to a slight decrease in support; the difference between the two messages is statistically significant ( p <.001). In combination with other results, this study's findings suggest that an implicit assumption of risk comparisons is in error: Opposition to controversial technologies may have little to do with citizens' levels of information about technology, having more to do with citizens' levels of trust in governmental and industrial actors.     

Varying Risk Comparison Elements: Effects on Public Reactions

Expanding a limited empirical base on effects of risk comparisons, a pilot experiment explored how varying elements of such comparisons might influence public response. The scenario used was a hypothetical trial of an asbestos-installing firm for putting students and staff at a junior high school at "unreasonable risk," first used by Slovic et al. (1990). Study participants played the role of jurors in the trial, asked to rate the risk, the firm's guilt, whether it should be made liable for future health effects, whether the school should be occupied in its current condition, and whether the asbestos should be removed at a cost of 3 million dollars. Opportunity samples of New Jersey residents (n= 309) received information intended to vary four comparison attributes: number of dimensions of comparison; single versus multiple ways of expressing mortality; a narrative to explain and justify the risk comparison; and the hypothetical role of the participant (juror vs. parent). The dependent variable was a hazard scale constructed from four of the five postcomparison judgments. ANOVA found format variations swamped in their effect by concern about asbestos, with the absence of a narrative and the parental role being the only attributes that increased negative risk reactions. Multiple regression analyses found that multidimensionality, narrative, role, and the presence of any risk comparison at all had significant effects when these (plus death formats) were the only independent variables. However, only multidimensionality (which increased negative reactions) retained significance when asbestos concern, risk beliefs (no safe level of exposure to a carcinogen; any exposure leads to cancer), and demographic variables were added to the analysis. Concern and risk beliefs alone explained 33% of variance in hazard scores; adding demographics and risk comparison variables only raised explained variance to 36% (having children at home and being exposed to multidimensional risk comparisons raised scores; age and income lowered them). The results underline the potentially small effect of risk comparison information on risk views (at least between subjects), but offer some insight into aspects of message design left unexplored in empirical literature to date.     

Improving Flood Risk Communication by Focusing on Prevention‐Focused Motivation

This article proposes an approach to flood risk communication that gives particular emphasis to the distinction between prevention and promotion motivation. According to E. Tory Higgins, the promotion system and the prevention system are assumed to coexist in every person, but one or the other may be temporarily or chronically more accessible. These insights have far‐reaching implications for our understanding of people's reasoning about risks. Flood risk communication framed in terms of prevention involves the notions of chance and harm, woven into a story about particular events that necessitate decisions to be more careful about safety issues and protect one's family and oneself from danger. The article describes how the insights worked out in practice, using a flood risk communication experiment among a sample from the general population in a highly populated river delta of the Netherlands. It had a posttest‐only control group design (n = 2,302). The results showed that risk communication had a large effect on the participants’ responses and that this effect was higher among chronic prevention‐focused people than among others. Any information that increased the fit between a prevention‐framed message and a person's chronic prevention motivation produced stronger situationally induced, prevention‐focused responses. This may significantly improve communication about risks. In contrast, the notion of water city projects, featuring waterside living, had more appeal to promotion‐focused people.     

Major Hazard Information Policy in the European Community: Implications for Risk Analysis

The main impetus to the development of information about major industrial hazards in the European Community comes from the so-called Seveso Directive, which defines an information network and requires the generation and transmission of information as the basis for accident prevention and risk management. This important policy development, which calls for the formal identification and analysis of major hazards and the communication of risk information to members of the public, presents new opportunities and challenges to risk analysis and research in Europe. This paper briefly reviews the accidents that gave rise to the Directive and shaped its content, and then summarizes its requirements. The status of its implementation in the EC Member States is discussed, with special emphasis given to the comparison of safety analysis practices, the Major Accident Reporting System (MARS), and risk communication. Some new research directions stimulated by the Directive are identified.     

Assessing Risk in Graphically Presented Financial Series

It has been argued that traders use their natural sensitivity to the fractal properties of price graphs to assess risk and that they are better able to do this when given price change as well as price level information. This approach implies that risk assessments should be higher when the Hurst exponents are lower, that this relationship should be stronger in the presence of price change information and that risk assessment should depend more strongly on the Hurst exponent than on the standard deviation of the series. Participants in Experiment 1 decided which of two assets was riskier by inspecting graphs of their price series. Graphs with lower Hurst exponents were selected only by those who were less emotionally stable and hence more sensitive to risk. However, when both price series and price change series were presented, the assets with lower Hurst exponents were selected by all participants. In a second experiment, participants were given both price level and price change series for a number of assets and rated the risk of trading in each one. Ratings depended more strongly on Hurst exponents than on other measures of volatility. They also depended on indicators of potential loss. Human risk assessment deviates from the way that risk is measured in modern finance theory: it requires integration of information relevant to both uncertainty and loss aversion, thereby imposing high attentional demands on traders. These demands may impair risk assessment but they can be eased by adding displays of price change information.     

Radon Testing Behavior in a Sample of Individuals with High Home Radon Screening Measurements

Although radon exposure has been identified as the second leading cause of lung cancer, fewer than 6% of U.S. homeowners test their homes for radon. This report examines participants'follow-up radon testing behavior subsequent to receiving an initial screening radon level greater than 20 pCi/L. Sixty-two participants in the Iowa State-Wide Rural Radon Screening Survey who had radon screening measurements over 20 pCi/L were questioned by phone survey 3 months after receipt of their radon screening result to assess: whether participants were aware of radon's health risk; if participants recalled the radon screening results; how participants perceived the relative health risk of radon and whether participants planned follow-up radon testing. Only 19% of the respondents specifically identified lung cancer as the possible adverse health outcome of high radon exposure, and the majority of participants underestimated the health risks high radon levels pose when compared to cigarettes and x-rays. In addition, less than one third (29%)of the participants actually remembered their radon screening level within 10 pCi/L 3 months after receiving their screening results. Only 53% of the individuals correctly interpreted their screening radon level as being in the high range, and only 39% of the participants planned follow-up radon measurements. Receipt of radon screening test results indicating high radon levels was not an adequate motivational factor in itself to stimulate further radon assessment or mitigation. Our findings suggest that free radon screening will not result in a dramatic increase in subsequent homeowner initiated remediation or further recommended radon testing.     

Communicating Worst-Case Scenarios: Neighbors'' Views of Industrial Accident Management

The prospect of industrial accidents motivated the U.S. Congress to require in the Clean Air Act of 1990 that manufacturing facilities develop Risk Management Plans (RMP) to submit to the U.S. Environmental Protection Agency (USEPA) by July 1999. Industry worried that the requirement to communicate to the public a "worst-case scenario" would arouse unnecessary and counterproductive fears among industry neighbors. We report here the results of focus groups and surveys with such neighbors, focusing particularly upon their reactions to messages about a hypothetical worst-case scenario and management of these risks by industry, government, and other parties. Our findings confirmed our hypotheses that citizens would be skeptical of the competence and trustworthiness of these managers and that this stance would color their views of industrial-facility accident risks. People with job ties to industry or who saw industrial benefits to the community as exceeding its risks had more positive views of industrial risks, but still expressed great concern about the risk and doubt about accident management. Notwithstanding these reactions, overall respondents welcomed this and other related information, which they wanted their local industries to supply. Respondents were not more reassured by additional text describing management of accidents by government and industry. However, respondents did react very positively to the concept of community oversight to review plant safety. Claims about the firm's moral obligation or financial self-interest in preventing accidents were also received positively. Further research on innovative communication and management of accident risks is warranted by these results, even before recent terrorist attacks made this topic more salient.