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G Gigerenzer

Publications and source records attributed to G Gigerenzer.

18 recordsLinked to original sources
PubMed2001

Content-blind norms, no norms, or good norms? A reply to Vranas.

In the psychology of thinking, little thought is given to what constitutes good thinking. Instead, normative solutions to problems have been accepted at face value, thereby determining what counts as a reasoning fallacy. I applaud Vranas (Cognition 76 (2000) 179) for thinking seriously about norms. I do, however, disagree with his attempt to provide post hoc justifications for supposed reasoning fallacies in terms of 'content-neutral' norms. Norms need to be constructed for a specific situation, not imposed upon it in a content-blind way. The reason is that content-blind norms disregard relevant structural properties of the given situation, including polysemy, reference classes, and sampling. I also show that content-blind norms can, unwittingly, lead to double standards: the norm in one problem is the fallacy in the next. The alternative to content-blind norms is not no norms, but rather carefully designed norms.

Cognition↗
PubMed2001

Teaching Bayesian reasoning in less than two hours.

The authors present and test a new method of teaching Bayesian reasoning, something about which previous teaching studies reported little success. Based on G. Gigerenzer and U. Hoffrage's (1995) ecological framework, the authors wrote a computerized tutorial program to train people to construct frequency representations (representation training) rather than to insert probabilities into Bayes's rule (rule training). Bayesian computations are simpler to perform with natural frequencies than with probabilities, and there are evolutionary reasons for assuming that cognitive algorithms have been developed to deal with natural frequencies. In 2 studies, the authors compared representation training with rule training; the criteria were an immediate learning effect, transfer to new problems, and long-term temporal stability. Rule training was as good in transfer as representation training, but representation training had a higher immediate learning effect and greater temporal stability.

Algorithms↗
PubMed2000

Medicine. Communicating statistical information.

Most people, experts included, have difficulties understanding and combining statistical information effectively. Hoffrage et al. demonstrate that these difficulties can be considerably reduced by communicating the information in terms of natural frequencies rather than in terms of probabilities. Several applications in medicine, legal decision-making, and education are discussed.

DNA Fingerprinting↗
PubMed2000

Précis of Simple heuristics that make us smart.

How can anyone be rational in a world where knowledge is limited, time is pressing, and deep thought is often an unattainable luxury? Traditional models of unbounded rationality and optimization in cognitive science, economics, and animal behavior have tended to view decision-makers as possessing supernatural powers of reason, limitless knowledge, and endless time. But understanding decisions in the real world requires a more psychologically plausible notion of bounded rationality. In Simple heuristics that make us smart (Gigerenzer et al. 1999), we explore fast and frugal heuristics--simple rules in the mind's adaptive toolbox for making decisions with realistic mental resources. These heuristics can enable both living organisms and artificial systems to make smart choices quickly and with a minimum of information by exploiting the way that information is structured in particular environments. In this précis, we show how simple building blocks that control information search, stop search, and make decisions can be put together to form classes of heuristics, including: ignorance-based and one-reason decision making for choice, elimination models for categorization, and satisficing heuristics for sequential search. These simple heuristics perform comparably to more complex algorithms, particularly when generalizing to new data--that is, simplicity leads to robustness. We present evidence regarding when people use simple heuristics and describe the challenges to be addressed by this research program.

Decision Making↗
PubMed2000

Hindsight bias: a by-product of knowledge updating?

With the benefit of feedback about the outcome of an event, people's recalled judgments are typically closer to the outcome of the event than their original judgments were. It has been suggested that this hindsight bias may be due to a reconstruction process of the prior judgment. A model of such a process is proposed that assumes that knowledge is updated after feedback and that reconstruction is based on the updated knowledge. Consistent with the model's predictions, the results of 2 studies show that knowledge after feedback is systematically shifted toward feedback, and that assisting retrieval of the knowledge prior to feedback reduces hindsight bias. In addition, the model accounts for about 75% of cases in which either hindsight bias or reversed hindsight bias occurred. The authors conclude that hindsight bias can be understood as a by-product of an adaptive process, namely the updating of knowledge after feedback.

Adult↗
PubMed2000

[How can one improve the understanding and communication of the importance of medical test results?].

Interpreting medical test results demands statistical reasoning on the part of doctors: How great is the probability of falsely diagnosing an illness based on a positive test result? This probability can be determined with the assistance of Bayes's Rule. Several studies show, however, that doctors often experience problems with these kinds of Bayesian inferences. We demonstrate that doctors' judgments can be considerably improved when numerical information is presented in a form easily accessible to the ways humans process information. This is not the case with the utilization of applied probabilities that has become customary, but is the case when the problem is presented in terms of "natural frequencies" that result from the counting of observed isolated cases in a natural environment. In a series of studies, we varied the representation format of the relevant statistical information. If the information was not presented in the form of probabilities or percentages but simply in natural frequencies, medical experts, as well as laymen, were able to improve their judgments significantly. And dealing with probabilities and percentages can also be easily learned: Two training programs, which showed how probabilities can be translated into natural frequencies, placed the participants in the position of being able to obtain very good results when solving these tasks. Finally, we discuss the impact of a comprehensible risk and utility communication on the doctor-patient relationship.

Bayes Theorem↗
PubMed1999

Specific attentional dysfunction in adults following early start of cannabis use.

RATIONALE AND OBJECTIVE: The present study tested the hypothesis that chronic interference by cannabis with endogenous cannabinoid systems during peripubertal development causes specific and persistent brain alterations in humans. As an index of cannabinoid action, visual scanning, along with other attentional functions, was chosen. Visual scanning undergoes a major maturation process around age 12-15 years and, in addition, the visual system is known to react specifically and sensitively to cannabinoids. METHODS: From 250 individuals consuming cannabis regularly, 99 healthy pure cannabis users were selected. They were free of any other past or present drug abuse, or history of neuropsychiatric disease. After an interview, physical examination, analysis of routine laboratory parameters, plasma/urine analyses for drugs, and MMPI testing, users and respective controls were subjected to a computer-assisted attention test battery comprising visual scanning, alertness, divided attention, flexibility, and working memory. RESULTS: Of the potential predictors of test performance within the user group, including present age, age of onset of cannabis use, degree of acute intoxication (THC+THCOH plasma levels), and cumulative toxicity (estimated total life dose), an early age of onset turned out to be the only predictor, predicting impaired reaction times exclusively in visual scanning. Early-onset users (onset before age 16; n = 48) showed a significant impairment in reaction times in this function, whereas late-onset users (onset after age 16; n = 51) did not differ from controls (n = 49). CONCLUSIONS: These data suggest that beginning cannabis use during early adolescence may lead to enduring effects on specific attentional functions in adulthood. Apparently, vulnerable periods during brain development exist that are subject to persistent alterations by interfering exogenous cannabinoids.

Adolescent↗
PubMed1998

AIDS counselling for low-risk clients.

This study addresses the counselling of heterosexual men with low-risk behaviour who, voluntarily or involuntarily, take an HIV test. If such a man tests positive, the chance that he is infected can be as low as 50%. We study what information counsellors communicate to clients concerning the meaning of a positive test and whether they communicate this information in a way the client can understand. To get realistic data, one of us visited as a client 20 public health centres in Germany to take 20 counselling sessions and HIV tests. A majority of the counsellors explained that false positives do not occur, and half of the counsellors told the client that if he tests positive, it is 100% certain that he is infected with the virus. Counsellors communicated numerical information in terms of probabilities rather than absolute frequencies, became confused and were inconsistent. Based on experimental evidence, we propose a simple method that counsellors can learn to communicate risks in a more effective way.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Using natural frequencies to improve diagnostic inferences.

PURPOSE: To test whether physician's diagnostic inferences can be improved by communicating information using natural frequencies instead of probabilities. Whereas probabilities and relative frequencies are normalized with respect to disease base rates, natural frequencies are not normalized. METHOD: The authors asked 48 physicians in Munich and Düsseldorf to determine the positive predictive values (PPVs) of four diagnostic tests. Information presented in the four problems appeared either as probabilities (the traditional way) or as natural frequencies. RESULTS: When the information was presented as probabilities, the physicians correctly estimated the PPVs in only 10% of cases. When the same information was presented as natural frequencies, that percentage increased to 46%. CONCLUSION: Representing information in natural frequencies is a fast and effective way of facilitating diagnosis insight, which in turn helps physicians to better communicate risks to patients, and patients to better understand these risks.

Bayes Theorem↗
PubMed1996

Reasoning the fast and frugal way: models of bounded rationality.

Humans and animals make inferences about the world under limited time and knowledge. In contrast, many models of rational inference treat the mind as a Laplacean Demon, equipped with unlimited time, knowledge, and computational might. Following H. Simon's notion of satisfying, the authors have proposed a family of algorithms based on a simple psychological mechanism: one-reason decision making. These fast and frugal algorithms violate fundamental tenets of classical rationality: They neither look up nor integrate all information. By computer simulation, the authors held a competition between the satisfying "Take The Best" algorithm and various "rational" inference procedures (e.g., multiple regression). The Take The Best algorithm matched or outperformed all competitors in inferential speed and accuracy. This result in an existence proof that cognitive mechanisms capable of successful performance in the real world do not need to satisfy the classical norms of rational inference.

Algorithms↗
PubMed1992

Domain-specific reasoning: social contracts, cheating, and perspective change.

What counts as human rationality: reasoning processes that embody content-independent formal theories, such as propositional logic, or reasoning processes that are well designed for solving important adaptive problems? Most theories of human reasoning have been based on content-independent formal rationality, whereas adaptive reasoning, ecological or evolutionary, has been little explored. We elaborate and test an evolutionary approach. Cosmides' (1989) social contract theory, using the Wason selection task. In the first part, we disentangle the theoretical concept of a "social contract" from that of a "cheater-detection algorithm". We demonstrate that the fact that a rule is perceived as a social contract--or a conditional permission or obligation, as Cheng and Holyoak (1985) proposed--is not sufficient to elicit Cosmides' striking results, which we replicated. The crucial issue is not semantic (the meaning of the rule), but pragmatic: whether a person is cued into the perspective of a party who can be cheated. In the second part, we distinguish between social contracts with bilateral and unilateral cheating options. Perspective change in contracts with bilateral cheating options turns P & not-Q responses into not-P & Q responses. The results strongly support social contract theory, contradict availability theory, and cannot be accounted for by pragmatic reasoning schema theory, which lacks the pragmatic concepts of perspectives and cheating detection.

Adult↗
PubMed1991

Probabilistic mental models: a Brunswikian theory of confidence.

Research on people's confidence in their general knowledge has to date produced two fairly stable effects, many inconsistent results, and no comprehensive theory. We propose such a comprehensive framework, the theory of probabilistic mental models (PMM theory). The theory (a) explains both the overconfidence effect (mean confidence is higher than percentage of answers correct) and the hard-easy effect (overconfidence increases with item difficulty) reported in the literature and (b) predicts conditions under which both effects appear, disappear, or invert. In addition, (c) it predicts a new phenomenon, the confidence-frequency effect, a systematic difference between a judgment of confidence in a single event (i.e., that any given answer is correct) and a judgment of the frequency of correct answers in the long run. Two experiments are reported that support PMM theory by confirming these predictions, and several apparent anomalies reported in the literature are explained and integrated into the present framework.

Adult↗
PubMed1983

Are there limits to binaural additivity of loudness?

In recent years there has been notable interest in additive models of sensory integration. Binaural additivity has emerged as a main hypothesis in the loudness-scaling literature and has recently been asserted by authors using an axiomatic approach to psychophysics. Restrictions of the range of stimuli used in the majority of former experiments, and inherent weaknesses of the axiomatic study by Levelt, Riemersma, and Bunt (1972) are discussed as providing reasons for the present investigation. A limited binaural additivity (LBA) model is proposed that assumes contralateral binaural inhibition for interaural intensity differences that exceed a critical level. Experimental data are reported for 12 subjects in a loudness-matching task designed to test the axioms of cancellation and of commutativity, both necessary to the existence of strict binaural additivity. In a 2 X 2 design, frequencies of 200 Hz and 2 kHz were used, and mean intensity levels were 20 dB apart. Additivity was found violated in 33 out of 48 possible tests. The LBA model is shown to predict the systematic nonadditivity in the loudness judgments and to conform to results from other studies.

Female↗
PubMed1982

[Modification of psychiatric diagnostic schemata by implicit nosological theories].

Diagnostic schemes of psychiatrists are explained by two components, a general explicit nosological theory and an individual implicit theory. An experimental study is devoted to the analysis of diagnostic schemes in three groups with different degrees of internalization of explicit nosological theory: (1) a non-psychiatrist group without nosological knowledge (2) a non-psychiatrist group, who obtained nosological knowledge in a 40-min session, and (3) a group of psychiatrists. Four structural components of diagnostic schemes were analyzed: stability, complexity, relevance for therapy of the individual diagnostic scheme, and interindividual homogeneity within groups. The diagnostic schemes of psychiatrists showed no more stability and relevance for therapy than those of group (2), whereas interindividual homogeneity as well as complexity were higher. Results indicate that the diagnostic schemes of psychiatrists are determined to a great extent by individual implicit theories.

Depressive Disorder↗
PubMed1982

[Psychiatric diagnosis and nosological theory: studies on the individual diagnostic schema of the physician].

This study is concerned with the diagnostic process of psychiatrists. Two concepts are investigated; the internalized nosological theory and the psychiatric diagnostic scheme. If patients or diseases are judged on predefined lists of symptoms (e.g. AMDP-list), we assume that judgments are based on the first one. If the psychiatrist, however, is free in the choice of relevant attributes in judging patients or diseases, we assume that his judgments are based on his individual diagnostic scheme. Results show high agreement in internalized nosological theories, but strong individual differences in diagnostic schemes. Interindividual agreement in internalized nosological theories is still greater than intraindividual agreement between diagnostic scheme and nosological theory. This proves that distinguishing the two concepts is meaningful. Structural components of both concepts, e.g., their dimensions, pregnant structures, and their metric, were analyzed by multidimensional scaling. We assume that the psychiatric diagnostic scheme determines the clinical diagnosis in everyday practice, whereas the internalized nosological theory is of importance mainly in research. The differences between both concepts suggest that lists of symptoms are not very helpful in analyzing clinical diagnosis. Thus, in order to achieve greater agreement in diagnosis, further and detailed analysis of individual "implicit" theories which determine the greater part of diagnostic schemes is necessary.

Alcoholism↗
PubMedDate not supplied

The psychology of good judgment: frequency formats and simple algorithms.

Mind and environment evolve in tandem--almost a platitude. Much of judgment and decision making research, however, has compared cognition to standard statistical models, rather than to how well it is adapted to its environment. The author argues two points. First, cognitive algorithms are tuned to certain information formats, most likely to those that humans have encountered during their evolutionary history. In particular, Bayesian computations are simpler when the information is in a frequency format than when it is in a probability format. The author investigates whether frequency formats can make physicians reason more often the Bayesian way. Second cognitive algorithms need to operate under constraints of limited time, knowledge, and computational power, and they need to exploit the structures of their environments. The author describes a fast and frugal algorithm. Take The Best, that violates standard principles of rational inference but can be as accurate as sophisticated "optimal" models for diagnostic inference.

Algorithms↗