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A complete understanding of decision-making in military domains requires gathering insights from several fields of study. To make the task tractable, here we consider a specific example of short-term tactical decisions under uncertainty made by the military at sea. Through this lens, we sketch out relevant literature from three psychological tasks each underpinned by decision-making processes: categorisation, communication and choice. From the literature, we note two general cognitive tendencies that emerge across all three stages: the effect of cognitive load and individual differences. Drawing on these tendencies, we recommend strategies, tools and future research that could improve performance in military domains – but, by extension, would also generalise to other high-stakes contexts. In so doing, we show the extent to which domain general properties of high order cognition are sufficient in explaining behaviours in domain specific contexts.

Effective risk communication about medical procedures is critical to ethical shared decision-making. Here, we explore the potential for development of an evidence-based lexicon for verbal communication of surgical risk. We found that Ear, Nose and Throat (ENT) surgeons expressed a preference for communicating such risks using verbal probability expressions (VPEs; e.g., "high risk"). However, there was considerable heterogeneity in the expressions they reported using (Study 1). Study 2 compared ENT surgeons' and laypeople's (i.e., potential patients) interpretations of the ten most frequent VPEs listed in Study 1. While both groups displayed considerable variability in interpretations, lay participants demonstrated more, as well as providing systematically higher interpretations than those of surgeons. Study 3 found that lay participants were typically unable to provide unique VPEs to differentiate between the ranges of (low) probabilities required. Taken together, these results add to arguments that reliance on VPEs for surgical risk communication is ill-advised. Not only are there systematic interpretational differences between surgeons and potential patients, but the coarse granularity of VPEs raises severe challenges for developing an appropriate evidence-based lexicon for surgical risk communication. We caution against the use of VPEs in any risk context characterized by low, but very different, probabilities. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

As food technology continues to advance, the potential for new food products to enter the food market grows, attracting considerable media interest. Whilst previous research has explored public per...

Background Typically, food-related risk assessments are carried out within a four step, technical framework, as detailed by the Codex Alimentarius Commission (World Health Organization/ Food and Agricultural Organization of the United Nations, 2015). However, the technical framework presumes a level of ‘objective risk’ and does not take into account that risk is complex and psychologically constructed, something which is rarely acknowledged within risk analysis as a whole. It is well documented that people's perceptions of risk are based on more than merely probability of occurrence, but reflect other non-technical psychological factors (e.g., risk origin, severity, controllability, familiarity). Moreover, the basis of these risk perceptions is largely similar for experts and non-experts. Scope and approach In this review, we consider each stage of the risk assessment process from a psychological perspective, reviewing research on non-technical factors which could affect assessments of risk and subsequent risk management decisions, with a particular focus on food safety. Key Findings and Conclusions We identify 12 factors from the psychological literature which could potentially influence how risks are assessed and characterised. Drawing on insights from this research, we propose a number of recommendations to standardise approaches in risk assessment. Acknowledging and working with the subjectivity of risk is key to ensuring the efficacy of the wider risk analysis process.

Risk communicators often need to communicate probabilistic predictions. On occasion, an event with 10% likelihood will occur, or one with 90% likelihood will not – a probabilistically unexpected ou...

Most of the claims we encounter in real life can be assigned some degree of plausibility, even if they are new to us. On Gilbert's (1991) influential account of belief formation, whereby understanding a sentence implies representing it as true, all new propositions are initially accepted, before any assessment of their veracity. As a result, plausibility cannot have any role in initial belief formation on this account. In order to isolate belief formation experimentally, Gilbert, Krull, and Malone (1990) employed a dual-task design: if a secondary task disrupts participants' evaluation of novel claims presented to them, then the initial encoding should be all there is, and if that initial encoding consistently renders claims 'true' (even where participants were told in the learning phase that the claims they had seen were false), then Gilbert's account is confirmed. In this pre-registered study, we replicate one of Gilbert et al.'s (1990) seminal studies ("The Hopi Language Experiment") while additionally introducing a plausibility variable. Our results show that Gilbert's 'truth bias' does not hold for implausible statements - instead, initial encoding seemingly renders implausible statements 'false'. As alternative explanations of this finding that would be compatible with Gilbert's account can be ruled out, it questions Gilbert's account.

How people update their beliefs when faced with new information is integral to everyday life. A sizeable body of literature suggests that people's belief updating is optimistically biased, such that their beliefs are updated more in response to good news than bad news. However, recent research demonstrates that findings previously interpreted as evidence of optimistic belief updating may be the result of flaws in experimental design, rather than motivated reasoning. In light of this controversy, we conduct three pre-registered variations of the standard belief updating paradigm (combined N = 300) in which we test for asymmetric belief updating with neutral, non-valenced stimuli using analytic approaches found in previous research. We find evidence of seemingly biased belief updating with neutral stimuli — results that cannot be attributed to a motivational, valence-based, optimism account — and further show that there is uninterpretable variability across samples and analytic techniques. Jointly, these results serve to highlight the methodological flaws in current optimistic belief updating research.

Understanding the scientific consensus on anthropogenic climate change has been dubbed a ‘gateway belief’ to engaging people in sustainable behaviour. We consider the question of how the impact of a consensus communication can be maximised. Firstly, the credibility of the communicator should be maximised. One way of achieving this is to present the opinions of a sample of scientists directly to individuals. The decision-making literature suggests that such a technique will confer an additional advantage over standard descriptions of consensus (e.g. ‘97% of scientists agree’). In decision-making research, low probabilities tend to be overweighted when probabilities are described, but underweighted when probability information is experienced. Consequently, statements of high consensus may lead to an overweighting of the dissensus, a phenomenon that may be reversed were the consensus to be ‘experienced.’ We obtain some positive support for our proposal that consensus is best ‘experienced’ in one of two experiments. We suggest that the lack of stronger positive support could relate to ceiling effects for the topics studied and propose that investigation of effective methods for ‘experiencing’ the consensus is a fruitful area for future research.

Evidence that context changes measured risk preferences raises concerns about the practice of measuring financial risk attitude in one context to guide investment choice. We found that participants who first made choices between pairs of high (low) risk pension funds subsequently preferred higher (lower) risk funds when offered a choice from a wider range of funds. This effect was also observed when the riskiness of the initial pension funds was manipulated within-subjects. Effects were not influenced by order, or attenuated by a bias warning. Tests across the domains of recreational and financial risk found that context effects are domain specific and that they influence both choices and judgments. Our results are consistent with theories of relative judgment. However, we also observed some evidence of sensitivity to absolute values. From an applied perspective, understanding such contextual sensitivity is important for recognising the limitations of risk profiling tools as part of a regulated financial advice process.

Calls to communicate uncertainty using mixed, verbal‐numerical formats (‘unlikely [0–33%]’) have stemmed from research comparing mixed with solely verbal communications. Research using the new ‘which outcome’ approach to investigate understanding of verbal probability expressions suggests, however, that mixed formats might convey disadvantages compared with purely numerical communications. When asked to indicate an outcome that is ‘unlikely’, participants have been shown to often indicate outcomes with a value exceeding the maximum value shown, equivalent to a 0% probability —an ‘extremity effect’. Recognising the potential consequences of communication recipients expecting an ‘unlikely’ event to never occur, we extend the ‘which outcome’ work across four experiments, using verbal, numerical, and verbal‐numerical communication formats, as well as a previously unconsidered numerical‐verbal format. We examine how robust the effect is in the context of consequential outcomes and over non‐normal distributions. We also investigate whether participants are aware of the inconsistency in their responses from a traditional ‘how likely’ and ‘which outcome’ task. We replicate and extend previous findings, with preference for extreme outcomes (including above maximum values) observed in both verbal and verbal‐numerical formats. Our results suggest caution in blanket usage of recently recommended verbal‐numerical formats for the communication of uncertainty.

ObjectivesThe aims of this study were (1) to document the clinical condition of patients considered to be in the last 2 weeks of life and (2) to compare patients who did or did not survive for 72 hours.DesignA prospective observational study.SettingTwo sites in London, UK (a hospice and a hospital palliative care team).ParticipantsAny inpatient, over 18 years old, English speaking, who was identified by the palliative care team as at risk of dying within the next 2 weeks was eligible.Outcome measuresPrognostic signs and symptoms were documented at a one off assessment and patients were followed up 7 days later to determine whether or not they had died.ResultsFifty participants were recruited and 24/50 (48%) died within 72 hours of assessment. The most prevalent prognostic features observed were a decrease in oral food intake (60%) and a rapid decline of the participant’s global health status (56%). Participants who died within 72 hours had a lower level of consciousness and had more care needs than those who lived longer. A large portion of data was unavailable, particularly that relating to the psychological and spiritual well-being of the patient, due to the decreased consciousness of the patient.ConclusionsThe prevalence of prognostic signs and symptoms in the final days of life has been documented between those predicted to die and those who did not. How doctors make decisions with missing information is an area for future research, in addition to understanding the best way to use the available information to make more accurate predictions.

The informational leakage account of attribute framing effects proposes that a communicator's choice of frame provides informational value, such that different frames are not informationally equivalent. Across five studies communicating food risks, we investigated the adaptability of communication recipients' (our participants) use of frame information by manipulating the degree to which the communicator ostensibly had a choice over how the information was framed. Within-participants framing effects were observed across all conditions of all studies. Only in Study 4 (the only study in which communicator choice was manipulated within-participants) was there any evidence for an attenuation of framing effects where the communicator was not responsible for how the information was framed. Overall, regardless of whether or not framing effects are driven by the informational value contained in a communicator's choice of frame, people show little sensitivity to situations where that choice is removed.

Verbal probability expressions (VPEs) are frequently used to communicate risk and uncertainty. The Intergovernmental Panel on Climate Change attempts to standardise the use and interpretation of these expressions through a translation scale of numerical ranges to VPEs. A common issue in interpreting VPEs is the tendency for individuals to interpret VPEs around the midpoint of the scale (i.e. around 50%). Previous research has shown that compliance with the IPCC’s standards can be improved if the numerical translation is presented simultaneously with the VPE, reducing the regressiveness of interpretations. We show that an explicit statement of the lower or upper bound implied by the expression (e.g. 0–33%; 66–100%) leads to better differentiated estimates of the probability implied by ‘likely’ and ‘unlikely’ than when the bound is not explicitly identified (e.g. less than 33%; greater than 66%).

Previous research suggests that people systematically overestimate the occurrence of both positive and negative events, compared with neutral future events, and that these biases are due to a misattribution of arousal elicited by utility (stake-likelihood hypothesis; SLH; Vosgerau, 2010). However, extant research has provided only indirect support for these arousal misattribution processes. In the present research, we initially aimed to provide a direct test of the SLH by measuring arousal with galvanic skin responses to examine the mediating role of arousal. We observed no evidence that measured arousal mediated the impact of utility on probability estimates. Given the lack of direct support for the SLH in Experiment 1, Experiments 2-5 aimed to assess the SLH by replicating some of the original findings that provided support for arousal misattribution as a mechanism. Despite our best efforts to create experimental conditions under which we would be able to demonstrate the stake-likelihood effect, we were unable to replicate previous results, with a Bayesian meta-analysis demonstrating support for the null hypothesis. We propose that accounts based on imaginability and loss function asymmetry are currently better candidate explanations for the influence of outcome utility on probability estimates.

Decision-making under conditions of uncertainty is present at every stage of the forensic process. The holistic and interactive nature of the different parts of the forensic science process as presented in this chapter, illustrates that decisions are not made in isolation. There is the potential for decisions and inferences made at one stage to impact a later stage and therefore, the ultimate judicial outcome of a case (Dror et al. 2017). It is therefore important to build the management of context effects on decision-making into every stage of the forensic process, not just the ‘interpretation’ stage.

Is the inferred preference of a deceased relative to donate his or her organs stronger when the choice was made under a mandated rather than under an automatic default (i.e., nudged choice) legislative system? The answer to this is particularly important, because families can, and do, veto the choices of their deceased relatives. In three studies, we asked American and European participants from countries that have either a default opt-in or a default opt-out system to take on the role of a third party to judge the likelihood that an individual's "true wish" was to actually donate his or her organs, given that the decedent was registered to donate on the organ donation register. In each study participants were randomly assigned to one of four organ donation legislative systems (default opt-in, default opt-out, mandated choice, mandatory). Overall, regardless of which country participants came from, they perceived the donor's underlying preference to donate as stronger under the default opt-in and mandated choice systems as compared with the default opt-out and mandatory donor systems. We discuss the practical issues that result from using default systems in the domain of organ donation and propose potential ways to ameliorate the uncertainty around inferences of underlying preference from a nudged choice. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Within UK policing it is routinely the responsibility of fingerprint laboratory practitioners to chemically develop areas of latent fingerprint ridge detail on evidential items and to determine which areas of ridge detail are of sufficient quality to be submitted to fingerprint experts for search or comparison against persons of interest. This study assessed the effectiveness of the fingermark submission process within the Evidence Recovery Unit Fingerprint Laboratory of the Metropolitan Police Service. Laboratory practitioners were presented with known source fingermark images previously deemed identifiable or insufficient by fingerprint experts, and were asked to state which of the marks they would forward to the Fingerprint Bureau. The results indicated that practitioners forwarded a higher percentage of insufficient fingermarks than is acceptable according to current laboratory guidelines, and discarded a number of marks that were of sufficient quality for analysis. Practitioners forwarded more insufficient fingermarks when considering fingermarks thought to be related to a murder and discarded more sufficient fingermarks when considering those thought to be related to a crime of ‘theft from vehicle’. The results highlight the need for fingerprint laboratories to work alongside fingerprint experts to ensure that a consistent approach to decision-making is, as far as possible, achieved, and that appropriate thresholds are adopted so as to prevent the loss of valuable evidence and improve the efficiency of the fingerprint filtering process.

The public expects science to reduce or eliminate uncertainty (Kinzig & Starrett, 2003), yet scientific forecasts are probabilistic (at best) and it is simply not possible to make predictions with certainty. Whilst an ‘unlikely’ outcome is not expected to occur, an ‘unlikely’ outcome will still occur one in five times (based on a translation of 20%, e.g. Theil, 2002), according to a frequentist perspective. When an ‘unlikely’ outcome does occur, the prediction may be deemed ‘erroneous’, reflecting a misunderstanding of the nature of uncertainty. Such misunderstandings could have ramifications for the subsequent (perceived) credibility of the communicator who made such a prediction. We examine whether the effect of ‘erroneous’ predictions on perceived credibility differs according to the communication format used. Specifically, we consider verbal, numerical (point and range [wide / narrow]) and mixed format probability expressions. We consistently find that subsequent perceptions are least affected by the ‘erroneous’ prediction when it is expressed numerically, regardless of whether it is a point or range estimate. Our findings suggest numbers should be used in consequential risk communications regarding ‘unlikely’ events, wherever possible.

In everyday situations, people regularly receive information from large groups of (lay) people and from single experts. Although lay opinions and expert opinions have been studied extensively in isolation, the present study examined the relationship between the two by asking how many laypeople are needed to counter an expert opinion. A Bayesian formalisation allowed the prescription of this quantity. Participants were subsequently asked to assess how many laypeople are needed in different situations. The results demonstrate that people are sensitive to the relevant factors identified for determining how many lay opinions are required to counteract a single expert opinion. People's assessments were fairly good in line with Bayesian predictions.

Bayesian probability has recently been proposed as a normative theory of argumentation. In this article, we provide a Bayesian formalisation of the ad Hitlerum argument, as a special case of the ad hominem argument. Across three experiments, we demonstrate that people's evaluation of the argument is sensitive to probabilistic factors deemed relevant on a Bayesian formalisation. Moreover, we provide the first parameter-free quantitative evidence in favour of the Bayesian approach to argumentation. Quantitative Bayesian prescriptions were derived from participants' stated subjective probabilities (Experiments 1 and 2), as well as from frequency information explicitly provided in the experiment (Experiment 3). Participants' stated evaluations of the convincingness of the argument were well matched to these prescriptions.

Adults and children have recently been shown to prefer guessing the outcome of a die roll after the die has been rolled (but remained out of sight) rather than before it has been rolled. This result is contrary to the predictions of the competence hypothesis (Heath & Tversky, 1991), which proposes that people are sensitive to the degree of their relative ignorance and therefore prefer to guess about an outcome it is impossible to know, rather than one that they could know, but do not. We investigated the potential role of agency in guessing preferences about a novel game of chance. When the experimenter controlled the outcome, we replicated the finding that adults and 5- to 6-year-old children preferred to make their guess after the outcome had been determined. For adults only, this preference reversed when they exerted control over the outcome about which they were guessing. The adult data appear best explained by a modified version of the competence hypothesis that highlights the notion of control or responsibility. It is proposed that potential attributions of blame are related to the guesser's role in determining the outcome. The child data were consistent with an imagination-based account of guessing preferences.

Repayment decisions—how much of the loan to repay and when to make the payments—directly influence consumer debt levels. The authors examine how minimum required payment policy and loan information disclosed to consumers influence repayment decisions. They find that while presenting minimum required payment information has a negative impact on repayment decisions, increasing the minimum required level has a positive effect on repayment for most consumers. Experimental evidence from U.S. consumers shows that consumers’ propensity to pay the minimum required each month moderates these effects; U.K. credit card field data indicate that borrowers’ credit limit and balance due also moderate these effects. However, increasing the minimum level is unlikely to completely eliminate the negative effect of presenting minimum payment information. In addition, disclosing supplemental information, such as future interest cost and time needed to repay the loan, does not reduce the negative effects of including minimum payment information and has no substantial positive effect on repayments. This research offers new insights into the debt repayment process and has implications for consumers, lenders, and public policy.

A robust finding in social psychology is that people judge negative events as less likely to happen to themselves than to the average person, a behavior interpreted as showing that people are "unrealistically optimistic" in their judgments of risk concerning future life events. However, we demonstrate how unbiased responses can result in data patterns commonly interpreted as indicative of optimism for purely statistical reasons. Specifically, we show how extant data from unrealistic optimism studies investigating people's comparative risk judgments are plagued by the statistical consequences of sampling constraints and the response scales used, in combination with the comparative rarity of truly negative events. We conclude that the presence of such statistical artifacts raises questions over the very existence of an optimistic bias about risk and implies that to the extent that such a bias exists, we know considerably less about its magnitude, mechanisms, and moderators than previously assumed.

IntroductionEvidence suggests that the majority of doctors are not very good at identifying when a patient is dying1 however there is little training available to improve this skill. Even experts are unable to articulate how they recognise when a patient is dying other than by saying that ‘I just knew’.2AimTo understand how expert palliative care doctors recognise a dying person.MethodsRather than relying on ‘years of experience’ as a surrogate measure of expertise we developed a test to identify which doctors really are the prognostic ‘experts’. The prognostic test consisted of 20 real patient case summaries. Participants (palliative care doctors) were asked to predict whether or not they expected the patient to die within the next 3 days. Those who were the most accurate at this task were deemed to be the ‘prognostic experts’ and were invited to complete an additional online judgement task. In this task it was possible to identify which factors were most influential in their prognostic decision-making.Results19/99 doctors who completed the prognostic test were deemed to be ‘experts’. Of those 14 also completed the additional judgement task. The following factors influenced the experts’ decisions: Cheyne Stokes breathing palliative performance score (PPS) a decline in condition in the previous 24 hours respiratory secretions cyanosis and level of agitation or sedation.ConclusionThis novel study presents a simple evidenced-based heuristic (or rule of thumb) to help novices recognise when a patient is imminently dying.References. Neuberger J, Guthrie C, Aaronovitch D. More care less pathway: A review of the Liverpool Care Pathway. Department of Health2013.. Taylor P, Dowding D, Johnson M. Clinical decision making in the recognition of dying: A qualitative interview study. BMC Palliative Care2017;16(1):11.

Possible measures to mitigate climate change require global collective actions whose impacts will be felt by many, if not all. Implementing such actions requires successful communication of the reasons for them, and hence the underlying climate science, to a degree that far exceeds typical scientific issues which do not require large-scale societal response. Empirical studies have identified factors, such as the perceived level of consensus in scientific opinion and the perceived reliability of scientists, that can limit people's trust in science communicators and their subsequent acceptance of climate change claims. Little consideration has been given, however, to recent formal results within philosophy concerning the relationship between truth, the reliability of evidence sources, the coherence of multiple pieces of evidence/testimonies, and the impact of (non-)independence between sources of evidence. This study draws on these results to evaluate exactly what has (and, more important, has not yet) been established in the empirical literature about the factors that bias the public's reception of scientific communications about climate change.

In this chapter, we provide a historical overview of research on bias in human cognition, ranging from early work in psychology through the detailed, quantitative examinations of belief revision in the 1960s, the Heuristic and Biases program initiated by Kahneman and Tversky, and bias focused research in personality and social psychology. Different notions of “bias” are identified and compared with the notion of bias in statistics, machine learning, and signal detection theory. Comparison with normative models then forms the basis for a critical look at the evidence that people succumb to motivated reasoning aimed at enabling them “to believe what they want to believe.”

Tackling climate change is a global challenge and the Intergovernmental Panel on Climate Change (IPCC) is the organisation charged with communicating the risks, dangers and mechanisms underlying climate change to both policy makers and the general public. The IPCC has traditionally used words (e.g., ‘likely’) in place of numbers (‘70 % chance’) to communicate risk and uncertainty information. The IPCC assessment reports have been published in six languages, but the consistency of the interpretation of these words cross-culturally has yet to be investigated. In two studies, we find considerable variation in the interpretation of the IPCC’s probability expressions between the Chinese and British public. Whilst British interpretations differ somewhat from the IPCC’s prescriptions, Chinese interpretations differ to a much greater degree and show more variation. These results add weight to continuing calls for the IPCC to make greater use of numbers in its forecasts.

Background Before being able to plan for end of life care, a doctor must first recognise that a patient is dying. A recent review has highlighted that doctors are not very good at this (Neuberger, 2013). Aim We set out to develop a “test” to assess how accurate doctors are at recognising dying. The test will consist of case studies, or “vignettes”, based on real palliative care patients. Methods In order to create the vignettes for the test, we undertook a prospective observational study of patients at two sites (a hospice and a hospital palliative care team). Any inpatient, over 18 years old, English speaking, and who was identified by the palliative care team as likely to die within the next two weeks was eligible. The clinical course of each patient was observed and was used to create a vignette, which formed the basis of the prognostic test. Results 50 participants were recruited and 20 were used to devise a prognostic test. For each vignette, clinicians were asked to assess the likelihood of death in the next 72 hours (scale 0% to 100%) based on the information presented. Illustrative examples of the test questions will be presented at the conference. Conclusions We have developed a standardised test to assess clinicians’ abilities to accurately diagnose imminent death. This test may be used to identify doctors who are most accurate at recognising dying. This may lead to an improved understanding of how this clinical skill is acquired and how it can be taught to less expert clinicians. Reference Neuberger J. More care, less pathway: a review of the Liverpool Care Pathway; 2013. Available at: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/212450/Liverpool_Care_Pathway.pdf

Philosophers have become increasingly interested in testimony (e.g. Coady, Testimony: A philosophical study. Oxford University Press, Oxford, 1992; Kusch & Lipton, Stud Hist Philos Sci 33:209–217). In the context of argumentation and persuasion, the distinction between the content of a message and its source is a natural and important one. The distinction has consequently attracted considerable attention within psychological research. There has also been a range of normative attempts to deal with the question of how source and message characteristics should combine to give rise to an overall evaluation of evidential strength (e.g. Walton, Witness testimony evidence: Argumentation, artificial intelligence, and law. Cambridge University Press, Cambridge, 2008). This chapter treats this issue from the perspective of the Bayesian approach to argument (Hahn & Oaksford, Psychol Rev 114:704–732, 2007a; Hahn et al., Informal Log 29:337–367, 2009) and summarises empirical evidence on key intuitions.

Verbal probability expressions are frequently used to communicate risk and uncertainty. The Intergovernmental Panel on Climate Change (IPCC), for example, uses them to convey risks associated with climate change. Given the potential for human action to mitigate future environmental risks, it is important to understand how people respond to these expressions. In 3 studies employing a novel manipulation of event severity (so as to avoid any confound with event base rate), we demonstrated a systematic effect of event severity on the interpretation of verbal probability expressions. Challenging a previous finding in the literature, expressions referring to a severe event were interpreted as indicating a higher probability than those referring to a more neutral event. The finding was demonstrated in scenarios communicating risks relating to climate change (Studies 1 and 2) and replicated in scenarios involving nanotechnology and nuclear materials (Study 3). This is the first direct demonstration of an effect of outcome severity on the interpretation of verbal probability expressions, correcting a previous (potentially problematic) conclusion attributable to a flawed experimental design. (PsycINFO Database Record (c) 2011 APA, all rights reserved). Language: en

Argumentation is pervasive in everyday life. Understanding what makes a strong argument is therefore of both theoretical and practical interest. One factor that seems intuitively important to the strength of an argument is the reliability of the source providing it. Whilst traditional approaches to argument evaluation are silent on this issue, the Bayesian approach to argumentation (Hahn & Oaksford, 2007) is able to capture important aspects of source reliability. In particular, the Bayesian approach predicts that argument content and source reliability should interact to determine argument strength. In this paper, we outline the approach and then demonstrate the importance of source reliability in two empirical studies. These experiments show the multiplicative relationship between the content and the source of the argument predicted by the Bayesian framework.

Routinely in day-to-day life, as well as in formal settings such as the courtroom, people must aggregate information they receive from different sources. One intuitively important but underresearched factor in this context is the degree to which the reports from different sources fit together, that is, their coherence. The authors examine a version of Bayes' theorem that not only includes factors such as prior beliefs and witness reliability, as do other models of information aggregation, but also makes transparent the effect of the coherence of multiple testimonies on the believability of the information. The results suggest that participants are sensitive to all the normatively relevant factors when assessing the believability of a set of witness testimonies.