Adam J. L. Harris

Estimating the probability of negative events

How well we are attuned to the statistics of our environment is a fundamental question in understanding human behaviour. It seems particularly important to be able to provide accurate assessments of the probability with which negative events occur so as to guide rational choice of preventative actions. One question that arises here is whether or not our probability estimates for negative events are systematically biased by their severity. In a minimal experimental context involving an unambiguous, objective representation of probability, we found that participants judged a controllable event as more likely to occur when its utility was extremely negative than when it was more neutral. A decision-theoretic explanation based on loss function asymmetries is advanced which supports the claim that probability estimates are not intrinsically biased by utilities.

Minimum Required Payment and Supplemental Information Disclosure Effects on Consumer Debt Repayment Decisions

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.

Communicating environmental risks: Clarifying the severity effect in interpretations of verbal probability expressions

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.

On the Origin of Utility, Weighting, and Discounting Functions: How They Get Their Shapes and How to Change Their Shapes

We present a theoretical account of the origin of the shapes of utility, probability weighting, and temporal discounting functions. In an experimental test of the theory, we systematically change the shape of revealed utility, weighting, and discounting functions by manipulating the distribution of monies, probabilities, and delays in the choices used to elicit them. The data demonstrate that there is no stable mapping between attribute values and their subjective equivalents. Expected and discounted utility theories, and also their descendants such as prospect theory and hyperbolic discounting theory, simply assert stable mappings to describe choice data and offer no account of the instability we find. We explain where the shape of the mapping comes from and, in describing the mechanism by which people choose, explain why the shape depends on the distribution of gains, losses, risks, and delays in the environment. Data, as supplemental material, are available at http://dx.doi.org/10.1287/mnsc.2013.1853 . This paper was accepted by Yuval Rottenstreich, judgment and decision making.

Management of Helicobacter pylori infection

This article discusses the current management of Helicobacter pylori infection in patients with dyspepsia with or without endoscopic abnormalities. We take an evidence based approach when possible and consider recent guidelines from national and international bodies pertaining to primary and secondary care. Microanatomy of gastric mucosa indicating the pH gradient In patients who are not taking non-steroidal anti-inflammatory drugs (NSAIDs) duodenal ulcer will be due to H pylori infection in 95% of cases, and eradication treatment can be prescribed without testing for H pylori. If there is any doubt about the diagnosis, such as a possible ulcer crater on a barium meal, endoscopic confirmation of duodenal ulcer and H pylori infection should be sought before prescribing treatment. Management plan for uncomplicated duodenal ulcer in patients not taking NSAIDs H pylori eradication treatment, if successful, will be effective in curing the ulcer diathesis regardless of whether a patient is seen at the initial presentation of the disease or at a recurrence. Patients taking long term (maintenance) treatment with H2 receptor antagonists or proton pump inhibitors should also be offered H pylori eradication treatment regardless of whether they are free of symptoms or still experiencing indigestion. In most cases eradication of H pylori cures the duodenal ulcer disease, and maintenance treatment can be stopped. ### After eradication treatment Uncomplicated duodenal ulcers heal quickly and completely after eradication of H pylori . Further antisecretory treatment, repeat endoscopy, or formal assessment of eradication is not necessary, and one can await the clinical outcome. Recurrent symptoms indicate either eradication failure or the presence of some other disease. Subsequent management will not be clear unless the outcome of eradication treatment is known, and this is best assessed by a 13C-urea breath test performed more than four weeks after the antimicrobial treatment. Recurrent symptoms after documented H pylori eradication …

A systematic review of predictions of survival in palliative care: How accurate are clinicians and who are the experts?

Background Prognostic accuracy in palliative care is valued by patients, carers, and healthcare professionals. Previous reviews suggest clinicians are inaccurate at survival estimates, but have only reported the accuracy of estimates on patients with a cancer diagnosis. Objectives To examine the accuracy of clinicians’ estimates of survival and to determine if any clinical profession is better at doing so than another. Data Sources MEDLINE, Embase, CINAHL, and the Cochrane Database of Systematic Reviews and Trials. All databases were searched from the start of the database up to June 2015. Reference lists of eligible articles were also checked. Eligibility Criteria Inclusion criteria: patients over 18, palliative population and setting, quantifiable estimate based on real patients, full publication written in English. Exclusion criteria: if the estimate was following an intervention, such as surgery, or the patient was artificially ventilated or in intensive care. Study Appraisal and Synthesis Methods A quality assessment was completed with the QUIPS tool. Data on the reported accuracy of estimates and information about the clinicians were extracted. Studies were grouped by type of estimate: categorical (the clinician had a predetermined list of outcomes to choose from), continuous (open-ended estimate), or probabilistic (likelihood of surviving a particular time frame). Results 4,642 records were identified; 42 studies fully met the review criteria. Wide variation was shown with categorical estimates (range 23% to 78%) and continuous estimates ranged between an underestimate of 86 days to an overestimate of 93 days. The four papers which used probabilistic estimates tended to show greater accuracy (c-statistics of 0.74–0.78). Information available about the clinicians providing the estimates was limited. Overall, there was no clear “expert” subgroup of clinicians identified. Limitations High heterogeneity limited the analyses possible and prevented an overall accuracy being reported. Data were extracted using a standardised tool, by one reviewer, which could have introduced bias. Devising search terms for prognostic studies is challenging. Every attempt was made to devise search terms that were sufficiently sensitive to detect all prognostic studies; however, it remains possible that some studies were not identified. Conclusion Studies of prognostic accuracy in palliative care are heterogeneous, but the evidence suggests that clinicians’ predictions are frequently inaccurate. No sub-group of clinicians was consistently shown to be more accurate than any other. Implications of Key Findings Further research is needed to understand how clinical predictions are formulated and how their accuracy can be improved.

What Does It Mean to be Biased: Motivated Reasoning and Rationality

Abstract 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.”

Testimony and argument: a Bayesian perspective

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.

The illusion of control: A Bayesian perspective

In the absence of an objective contingency, psychological studies have shown that people nevertheless attribute outcomes to their own actions. Thus, by wrongly inferring control in chance situations people appear to hold false beliefs concerning their agency, and are said to succumb to an illusion of control (IoC). In the current article, we challenge traditional conceptualizations of the illusion by examining the thesis that the IoC reflects rational and adaptive decision making. Firstly, we propose that the IoC is a by-product of a rational uncertain judgment (“the likelihood that I have control over a particular outcome”). We adopt a Bayesian perspective to demonstrate that, given their past experience, people should be prone to ascribing skill to chance outcomes in certain situations where objectively control does not exist. Moreover, existing empirical evidence from the IoC literature is shown to support such an account. Secondly, from a decision-theoretic perspective, in many consequential situations, underestimating the chance of controlling a situation carries more costs than overestimating that chance. Thus, situations will arise in which people will incorrectly assign control to events in which outcomes result from chance, but the attribution is based on rational processes.

Public Reception of Climate Science: Coherence, Reliability, and Independence

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 peoples 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 publics reception of scientific communications about climate change.