Nigel Harvey

Blackwell handbook of judgment and decision making.

The Handbook * Contains contributions by experts from various disciplines that reflect current trends and controversies on judgment and decision making. * Provides a glimpse at the many approaches that have been taken in the study of judgment and decision making and portrays the major findings in the field. * Presents examinations of the broader roles of social, emotional, and cultural influences on decision making. * Explores applications of judgment and decision making research to important problems in a variety of professional contexts, including finance, accounting, medicine, public policy, and the law.

Context-sensitive heuristics in statistical reasoning

Previous work has shown that people use anchor-and-adjust heuristics to forecast future data points from previous ones in the same series. We report three experiments that show that they use different versions of this heuristic for different types of series. To forecast an untrended series, our subjects always took a weighted average of the long-term mean of the series and the last data point. In contrast, the way that they forecast a trended series depended on the serial dependences in it. When these were low, people forecast by adding a proportion of the last difference in the series to the last data point. When stronger serial dependences made this difference less similar to the next one, they used a version of the averaging heuristic that they employed for untrended series. This could take serial dependences into account and included a separate component for trend. These results suggest that people use a form of the heuristic that is well adapted to the nature of the series that they are forecasting. However, we also found that the size of their adjustments tended to be suboptimal. They overestimated the degree of serial dependence in the data but underestimated trends. This biased their forecasts.

Graphs versus tables: Effects of data presentation format on judgemental forecasting

Abstract We report two experiments designed to study the effect of data presentation format on the accuracy of judgemental forecasts. In the first one, people studied 44 different 20-point time series and forecast the 21st and 22nd points of each one. Half the series were presented graphically and half were in tabular form. Root mean square error ( RMSE ) in forecasts was decomposed into constant error (to measure bias) and variable error (to measure inconsistency). For untrended data, RMSE was somewhat higher with graphical presentation: inconsistency and an overforecasting bias were both greater with this format. For trended data, RMSE was higher with tabular presentation. This was because underestimation of trends with this format was so much greater than with graphical presentation that it overwhelmed the smaller but opposing effects that were observed with untrended series. In the second experiment, series were more variable but very similar results were obtained.

Non-informative effects of stimuli functioning as cues

The category of a first stimulus (S1) serving as a cue may allow a subject to predict the category of a second stimulus (S2). However, a cue may have effects on RT to S2 that are independent of those derived from its intended role as a predictor. These non-informative effects of a cue may add to or subtract from the benefits associated with its predictive function. Two experiments demonstrate that when S1 is in the same category as S2 (as is frequently the case for valid cues in cueing experiments) but provides no information about S2, RT is slower than when S1 is in a different category from S2. It is suggested that this category relation effect arises because inhibition of a response to S1 is still present when S2 arrives and that, in some cueing experiments, it may subtract from the RT benefits derived from the cue as a predictor of S2. Also, RT to a visual but not to an auditory S2 was faster after an auditory S1 than after a visual S1. It is argued that this modality combination effect is consistent with the view that auditory signals are more alerting than visual ones and that this is another factor to be taken into account in the design of cueing and other experiments.

Combining forecasts: What information do judges need to outperform the simple average?

Abstract Previous work has shown that combinations of separate forecasts produced by judgment are inferior to those produced by simple averaging. However, in that research judges were not informed of outcomes after producing each combined forecast. Our first experiment shows that when they are given this information, they learn to weight the separate forecasts appropriately. However, their judgments, though improved, are still not significantly better than the simple average because they contain a random error component. Bootstrapping can be used to remove this inconsistency and produce results that outperform the average. In our second and third experiments, we provided judges with information about errors made by the individual forecasters. Results show that providing information about their mean absolute percentage errors updated each period enables judges to combine their forecasts in a way that outperforms the simple average.

Which doctors are influenced by a patient’s age? A multi-method study of angina treatment in general practice, cardiology and gerontology

Background: Elderly patients with cardiovascular disease are relatively undertreated and undertested. Objectives: To investigate whether, and how, individual doctors are influenced by a patient’s age in their investigation and treatment of angina. Design: Process-based judgment analysis using electronic patients, semistructured interviews. Setting: Primary Care, Care of the Elderly and Cardiology in England. Participants: Eighty five doctors: 29 cardiologists, 28 care of the elderly specialists and 28 general practitioners (GPs). Main outcome measures: Testing and treatment decisions on hypothetical patients. Results: Forty six per cent of GPs and care of the elderly doctors, and 48% of cardiologists treated patients aged 65+ differently to those under 65, independent of comorbidity. This effect was evident on several decisions: elderly patients were less likely to be prescribed a statin given a cholesterol test, referred to a cardiologist, given an exercise tolerance test, angiography and revascularisation; more likely to have their current prescriptions changed and to be given a follow-up appointment. There was no effect of specialty, gender or years of training on influence of patient age. Those doctors who were influenced by age were on average five years older than those who were not. Interviews revealed that some doctors saw old age as a contraindication to treat. Conclusions: Age, independent of comorbidity, presentation and patients’ wishes, directly influenced decision-making about angina investigation and treatment by half of the doctors in the primary and secondary care samples. Doctors explicitly reasoned about the direct influence of age and age-associated influences.

Biased Forecasting of Postdecisional Affect

Although anticipated postdecisional regret is a significant contributor to peoples decision-making processes, the accuracy of peoples regret forecasts has yet to be assessed systematically. Here we report two studies to fill this lacuna. In Study 1, we found that subjects who made reasonably high offers overpredicted the regret that they experienced after they unexpectedly failed at a negotiation. In Study 2, we found that subjects overpredicted the rejoicing and marginally underpredicted the regret that they experienced when they received higher marks than they had expected for their course work. Systematic affective misprediction implies that people making decisions should discount the regret and rejoicing that they anticipate will be associated with potential outcomes arising from those decisions.

Predicting preferences: a neglected aspect of shared decision-making

In recent years, shared decision‐making between patients and doctors regarding choice of treatment has become an issue of priority. Although patients’ preferences lie at the core of the literature on shared decision‐making, there has not been any attempt so far to link the concept of shared decision‐making with the extensive behavioural literature on peoples self‐predictions of their future preferences. The aim of the present review is to provide this link. First, we summarize behavioural research that suggests that people mispredict their future preferences and feelings. Secondly, we provide the main psychological accounts for peoples mispredictions. Thirdly, we suggest three main empirical questions for inclusion in a programme aimed at enriching our understanding of shared decision‐making and improving the procedures used for putting it into practice.

Regret triggers inaction inertia--but which regret and how?

When people miss a good bargain, they are less likely to take a subsequent one that is not as good. This phenomenon is termed inaction inertia. Two regret-based explanations of it have been proposed. According to one, people anticipate that buying the item will lead to regret because it will remind them that they missed a better opportunity to buy it. According to the other, the regret people experience when missing a bargain, together with a subjective devaluation of the item resulting from that, produces inaction inertia. In two studies, we assessed experienced regret, anticipated regret, subjective valuation (SV) of the bargain and likelihood of purchase. Our findings provide grounds for reconciling the above accounts. The former is more appropriate when the difference between the previous and subsequent bargain is large, and the latter is more appropriate when it is smaller. Furthermore, our findings suggest that previous accounts of inaction inertia are incomplete. Whereas subjective value and regret considerations jointly determine purchase likelihood when no previous opportunity has been missed, regret considerations are the sole determinant of this likelihood when such an opportunity has been missed. Inaction inertia arises at least partly because considering regret turns attention away from the financial advantages of taking the bargain.

Confidence Judgments by Actors and Observers

We report three experiments comparing confidence judgments made by actors and by observers. In Experiment 1, actors generated qualitative answers (countries of the world) in a country-identification task; in Experiment 2, actors generated quantitative answers (years) in a historical event-dating task. Both actors and observers indicated their confidence in the actors’ answers. Actors were significantly less confident in their answers than were observers in the first experiment. This eAect was substantially reduced in the second experiment, whether confidence was measured by judged probability or by credible interval width. Experiment 3 used a control task in which actors attempted to bring an outcome variable into a desired range. In contrast to the first two experiments, actors in the control task were more confident than observers. Because subjects were generally overconfident in all three experiments, the present results demonstrate that the use of observers can reduce or exacerbate overconfidence depending on the kind of task and the nature of the event or possibility under evaluation. #1997 by John Wiley & Sons, Ltd.