Willem A. Wagenaar

Accidents at sea: multiple causes and impossible consequences

Abstract Accidents are the consequences of highly complex coincidences. Among the multitude of contributing factors human errors play a dominant role. Prevention of human error is therefore a promising target in accident prevention. The present analysis of 100 accidents at sea shows that human errors were not as such recognizable before the accident occurred. Therefore general increase of motivation or of safety awareness will not remedy the problem. The major types of human error that contribute to the occurrence of accidents are wrong habits, wrong diagnoses, lack of attention, lack of training and unsuitable personality. These problems require specific preventive measures, directed at the change of undesired behaviors. Such changes should be achieved without the requirement that people comprehend the relation between their actions and subsequent accidents.

Does the expert know? The reliability of predictions and confidence ratings of experts

Experts are often asked to assess two different kinds of probabilities. One is THE PROBABILITY THAT SOMETHING WILL HAPPEN: rain, hitting an oil well, dying in an operation, tube fracture, a total melt-down. We will call these probabilities “predictions”. Experts’ predictions are widely used in all sorts of personal and public decision making. Two examples of formal usage of expert opinion are risk analyses and expert systems used for diagnostic tasks. The second kind of probability assessed by experts is THE PROBABILITY THAT THEIR ANSWERS ARE CORRECT. We will call these probabilities “confidence ratings”. A little later we will demonstrate that predictions and confidence ratings have often been confused in the literature.

The pond-and-duckweed problem; Three experiments on the misperception of exponential growth

Abstract The representation of duckweed multiplying itself in a pond is used as a research paradigm to study underestimation of exponential growth. The advantage of this paradigm is that the growth process is presented in a direct non-numerical way. The results show that the underestimation observed in earlier studies where growth was presented by means of tables or graphs, occurs in the pond-and-duckweed situation as well. By manipulating the way the process is presented it is possible to obtain some insight into the sampling strategies used by the subjects when they subjectively extrapolate the perceived processes. These experiments lead to the conclusion that subjects base their extrapolations on three or four samples only.

Tripod Delta: Proactive Approach to Enhanced Safety

Tripod Delta (diagnostic evaluation tool for accident prevention) is a checklist-based approach to carrying out safety health checks. This paper describes the theoretical background of the approach, which is based on a model for understanding the role of human error in accidents. The method for constructing databases from which to make checklists and use of the system to generate remedial safety plans are described. Finally, the implementation is discussed and the status is reviewed.

The proper seat

The role of social scientists as expert witnesses is controversial because, for instance, social science is thought to involve too many uncertainties, or because science is viewed as incompatible with the adversary process of courtroom argumentation. This paper argues that the controversy stems from a confusion between the opinions formed in the minds of the members of a court, and the information on which these opinions are based. Within the framework of Bayesian decision theory these two notions are distinguished. When the task of expert witnesses is limited to providing information (likelihoods in Bayesian terminology), the danger that social scientists will misrepresent the reliability of their knowledge or make biased statements is not larger than in the normal conduct of their science.

Islanders and hostages: Deep and surface structures of decision problems☆

Abstract Decision problems can be characterized by their surface structure (the story as presented) and their deep structure (the representation of the problem used by a respondent or as specified by a psychological theory). We started with a story problem about an island with a life-threatening epidemic. The authors of this problem (Hammerton, Jones-Lee and Abbott 1982) assumed a deep structure based on subjectively expected utility (SEU) theory and concluded that a large majority of their respondents were risk averse. We developed eleven variations of the surface structure, all of which could be represented by the same deep structure. The responses of 1,366 Dutch, American, and Israeli subjects varied widely as a function of some of these surface changes, indicating that underlying deep structure was not at all like the simple SEU representation. The translation from surface structure to deep structure can be quite complex; researches should not make untested assumptions about this translation when using story problems to test their theories.

Types and tokens in road accident causation

Accidents are preceded by long histories containing multitudes of events that constitute promising targets for preventive action. These antecedent events can be classified into at least four groups that occur in this order: failure types; psychological precursors; unsafe acts; and breakdown of defences. It is argued that events directly preceding an accident, such as breakdown of defences and unsafe acts, are only haphazard tokens of the more permanent weaknesses within a system, called failure types. Elimination of a type will therefore have much more impact than the elimination of one or a few tokens. It is also argued that there exist only a limited number of failure types, which are responsible for all accidents. However, in the specific area of road accidents, it is not known which types cause most of the problems. Therefore, their relative importance can only be guessed. We guessed that hardware problems and maintenance are unimportant types; that education and regulations are of moderate importance...

Calibration and the effects of knowledge and reconstruction in retrieval from memory

Abstract In this paper a distinction is made between retrieval of information that is actually stored in memory and reconstruction of information on the basis of inferential reasoning. Past research suggests that the relation between recall accuracy and confidence is good in the case of direct retrieval but poor in the case of reconstruction. Hence this relation, portrayed by calibration plots, might reveal the nature of the recall process. In three successive experiments conditions are created in which reconstruction on the basis of plausible cues would be likely. For these conditions it was predicted that calibration should be poor. The results confirm the predictions. Moreover, some independent evidence indicating that responses were based on reconstruction was obtained from the fact that accuracy scores repeatedly dropped significantly below guessing level.

Calibration of probability assessments by professional blackjack dealers, statistical experts, and lay people.

Abstract The question addressed in this study is whether experts are better calibrated than lay people. We investigated how well people are calibrated when they assess the probabilities of card combinations in the game of blackjack. Three groups of subjects were used: professional dealers, statistical experts, and control subjects. The results showed that experience and statistical expertise do not make people better calibrated in this task. It is argued that the concept of calibration is not wholly appropriate to describe the obtained deviations from the normatively correct responses. This is illustrated by a discriminant analysis performed on the signed deviation scores, which resulted in an almost perfect separation of the three groups, although they were overlapping with respect to calibration.

The Misinformation Effect: Transformations in Memory Induced by Postevent Information

When people encounter misleading information after they view an event, their recollection of the event is often affected (see Loftus, Miller, & Burns, 1978; Bekerian & Bowers, 1983; for examples). We refer to the change in report arising from postevent misinformation as the misinformation effect. In thinking about the impact of misinformation, it is useful to distinguish between a memory report (or what people claim to remember), and a memory trace (or what memory information is stored in the brain). Because the memory traces themselves are, obviously, never directly accessible to researchers, we must rely on memory reports to give us clues about the nature of the underlying trace.