Evidence for rule-based processes in the inverse base-rate effect.

Three studies provide convergent evidence that the inverse base-rate effect (Medin & Edelson, 1988) is mediated by rule-based cognitive processes. Experiment 1 shows that, in contrast to adults, prior to the formal operational stage most children do not exhibit the inverse base-rate effect. Experiments 2 and 3 demonstrate that an adult sample is a mix of participants relying on associative processes who categorize according to the base-rate and participants relying on rule-based processes who exhibit a strong inverse base-rate effect. The distribution of the effect is bimodal, and removing participants independently classified as prone to rule-based processing effectively eliminates the inverse base-rate effect. The implications for current explanations of the inverse base-rate effect are discussed.     

No evidence for rule-based processing in the inverse base-rate effect

The inverse base-rate effect in categorization (Medin & Edelson, 1988) arises when participants assign an ambiguous stimulus to a category that occurred less frequently than an alternative category, against the principles of Bayesian decision making. In the experiment reported in this article, rule-based and attention-shifting accounts of the inverse base-rate effect were evaluated. Participants completed a categorization task, known to produce the inverse base-rate effect, under standard conditions, under time pressure, and with a secondary task load. The inverse base-rate effect persisted under severe time pressure and under secondary task load. The results provided no evidence for the role of rule-based processes in producing the inverse base-rate effect. The data from the experiment are compatible with an attention-shifting account.     

Featural selective attention,exemplar representation,and the inverse base-rate effect

Selective attention plays a central role in theories of category learning and representation. In exemplar theory, selective attention has typically been formalized as operating uniformly across entire stimulus dimensions. Selective featural attention operating within dimensions has been recognized as a conceptual possibility, but relatively little research has focused on evaluating it. In the present research, we explored the usefulness of selective featural attention in the context of exemplar representation. We report the results of embedding the feature-to-category relations typically associated with the inverse base-rate effect—a classic and paradoxical category-learning result— perceptual category-learning task using a category structure with three multivalued feature dimensions. An exemplar model incorporating featural selective attention accurately accounted for the inverse base-rate effect that occurred but failed to do so with only dimensional attention.     

Diagnosticity and the base-rate effect

A common judgmental task involves predicting the category membership of an individual on the basis of information specific to that individual and background information regarding the base rate of different categories. According to statistical theory, predictions may deviate from base rates only to the extent that the individuating information is diagnostic. Previous research has demonstrated that diagnosticity is often judged by “representativeness,” the degree to which the individuating information is differentially suggestive of the different possible categories. Thus, information with high differential representativeness will swamp base-rate information even if it is almost worthless (e.g., because its source is unreliable). The present studies varied differential representativeness by manipulating the prediction categories’ similarity to one another vis-a-vis the individuating information. It was found that the effect of the base rate increased systematically as differential representativeness decreased. Representativeness was measured independently by several converging techniques. These measures predicted the magnitude of the base-rate effect, supporting the hypothesis that neutral stimuli are assigned to categories in proportion to the base rates.     

心理距离对基线比例忽略的影响

基线比例忽略是指在不确定情境中, 个体进行判断和决策时不能充分利用或者忽略基线比例的现象。本研究通过系列情境实验探索了三种不同维度的心理距离, 即时间距离、空间距离和社会距离对基线比例忽略的影响。结果发现, 三种心理距离均能够对基线比例忽略产生影响：当时间距离、空间距离和社会距离较近时, 个体更容易表现出基线比例忽略现象; 而当时间距离、空间距离和社会距离较远时, 个体的基线比例忽略倾向减弱。     

The frequency and effect on outcome of different types of interpretation in psychodynamic and cognitive-behavioral group psychotherapy

The therapeutic effects of interpretations by both therapists and other clients were recorded by observers in three cognitive-behavioral and three psychodynamic groups over a period of thirty one-and-one-half-hour group therapy sessions. There was no significant difference in the overall frequency of interpretations made in the two different therapy modalities; however, there was the expected difference in the types of interpretations made. Cognitive-behavior therapists and group members tended to interpret patterns of behavior or impact on others more frequently than did psychodynamic therapists and group members; while psychodynamic therapists and group members made more historical cause interpretations. However, contrary to expectations, both therapy modalities made more interpretations of patterns of present behavior than any other type. When these interpretations were converted into problem statements that were sent to outside raters after the termination of the groups, the outside raters judged that clients improved most when interpretations of a pattern of behavior were made; next most when interpretations of impact on others were made; and did not improve when interpretations of motive were employed in either modality.     

Context and the inverse base rate effect

Recent categorization research set in abstract medical diagnosis contexts has demonstrated an ‘inverse base rate effect’, whereby subjects make diagnoses which are consistent with base rates when presented with some sets of symptoms, but inconsistent with base rates when presented with other sets of symptoms. This paper reports three experiments which demonstrate that whether or not the inverse base rate effect is observed depends on the context in which categorization takes place. Inverse base rate effects are replicated in the abstract medical diagnosis context used in prior research, but not in a relatively realistic financial auditing setting, a less realistic financial auditing setting, or a very abstract generic setting. These results indicate that the inverse base rate effect may not generalize to applied settings, suggesting that interventions designed to mitigate the inverse base rate effect should not be instituted without first determining the existence of the effect in the particular setting in question.     

Problem structure and the use of base-rate information from experience

This article is concerned with the use of base-rate information that is derived from experience in classifying examples of a category. The basic task involved simulated medical decision making in which participants learned to diagnose hypothetical diseases on the basis of symptom information. Alternative diseases differed in their relative frequency or base rates of occurrence. In five experiments initial learning was followed by a series of transfer tests designed to index the use of base-rate information. On these tests, patterns of symptoms were presented that suggested more than one disease and were therefore ambiguous. The alternative or candidate diseases on such tests could differ in their relative frequency of occurrence during learning. For example, a symptom might be presented that had appeared with both a relatively common and a relatively rare disease. If participants are using base-rate information appropriately (according to Bayes' theorem), then they should be more likely to predict that the common disease is present than that the rare disease is present on such ambiguous tests. Current classification models differ in their predictions concerning the use of base-rate information. For example, most prototype models imply an insensitivity to base-rate information, whereas many exemplar-based classification models predict appropriate use of base-rate information. The results reveal a consistent but complex pattern. Depending on the category structure and the nature of the ambiguous tests, participants use base-rate information appropriately, ignore base-rate information, or use base-rate information inappropriately (predict that the rare disease is more likely to be present). To our knowledge, no current categorization model predicts this pattern of results. To account for these results, a new model is described incorporating the ideas of property or symptom competition and context-sensitive retrieval.     

Individual versus group use of base-rate and individuating information

This study compared individual and group use of base-rate and individuating information. Individuals and five-person groups were presented with base-rate information and with individuating information and were asked to judge probabilities. Results indicate that groups report relying on the individuating information significantly more and on the base rate significantly less than individuals. The probability judgments of groups are more sensitive to subjects' beliefs about what the individuating information sounds like than the judgments of individuals. There is some evidence that the probability judgments of groups are more extreme than those of individuals. Group discussion appears to amplify the tendency of individuals to judge by representativeness when assessing category membership.     

词频与阅读方式对词跨行呈现效应的影响

通过使用眼动追踪技术,采用2（呈现条件：同行呈现、跨行呈现）×2（词频：高频、低频）×2（阅读方式：朗读、默读）的被试内实验设计,探讨了词频和阅读方式对词跨行呈现效应的影响。结果发现,呈现条件、词频和阅读方式的主效应显著,跨行呈现、低频和朗读的凝视时间和总注视时间更长、总注视次数更多;呈现条件之间在凝视时间上的差异,高频词大于低频词;呈现条件之间在凝视时间和总注视次数上的差异,朗读大于默读。结果表明,词跨行呈现干扰了阅读,且这种干扰作用受词频和阅读方式的影响。     

Effects of study list composition on the word frequency effect and metacognitive attributions in recognition memory

In two experiments, study-list composition was manipulated and its impact was observed on metacognitive judgements associated with recognition hits (Hs) and false alarms (FAs). Both studies involved recognition of high-frequency (HF) and low-frequency (LF) words, and focused on the FA portion of the word frequency effect. Our hypothesis was that participants can actively reject items that are distinctive from the study list, and that this effect may be strong enough to overcome the FA word frequency effect. Experiment 1 manipulated list composition with a conjunctive rule and Experiment 2 varied it by having participants study either HF or LF items prior to a test consisting of words of both frequencies. In each study H rate, FA rate, and metacognitive attributions underlying recognition decisions were investigated. In both studies, participants reported rejecting test items predominantly through a process of active rejection, which was more often reported for LF items. This effect was strong enough to reverse the FA portion of the word frequency effect in Experiment 2, but not Experiment 1. The results are discussed in terms of metacognitive rejection mechanisms in recognition memory.     

Effects of study list composition on the word frequency effect and metacognitive attributions in recognition memory

In two experiments, study-list composition was manipulated and its impact was observed on metacognitive judgements associated with recognition hits (Hs) and false alarms (FAs). Both studies involved recognition of high-frequency (HF) and low-frequency (LF) words, and focused on the FA portion of the word frequency effect. Our hypothesis was that participants can actively reject items that are distinctive from the study list, and that this effect may be strong enough to overcome the FA word frequency effect. Experiment 1 manipulated list composition with a conjunctive rule and Experiment 2 varied it by having participants study either HF or LF items prior to a test consisting of words of both frequencies. In each study H rate, FA rate, and metacognitive attributions underlying recognition decisions were investigated. In both studies, participants reported rejecting test items predominantly through a process of active rejection, which was more often reported for LF items. This effect was strong enough to reverse the FA portion of the word frequency effect in Experiment 2, but not Experiment 1. The results are discussed in terms of metacognitive rejection mechanisms in recognition memory.     

The base-rate fallacy in the context of sequential categories

Three experiments assessed base-rate utilization in a paradigm in which the relevant categories of the population were trials in sequences of variable length. In one version of stimulus materials, for example, a trial was represented by a toss of a coin, and a sequence was a series of coin tosses. Since each described sequence was to end upon the scoring of a “hit” in any trial, the likelihood of a trial’s being attempted was a decreasing function of its position in the sequence. Subjects who estimated the particular trial upon which the hit in a sequence was most likely to occur showed a significant tendency to ignore the probable higher prevalence—the greater base rate— of early trials in the overall population of atttempts, typically estimating that the hit in the sequence was equally likely on any trial. This tendency, however, was modified by the specific problem context. In all experiments, significantly more normatively correct estimates were made in the coin context, in which the disparity between base rates of early trials and later trials was most pronounced. Although subjects in the third experiment who had previously taken a statistics course displayed superior performance on the coin problem, there was no evidence of transfer of this superiority to another context. These results are interpreted within the theoretical framework of the base-rate fallacy. In particular, the article discusses implications of the finding that general base rates may be ignored even in the absence of specific diagnostic indicators.     

Social stereotypes and judgments of individuals: An instance of the base-rate fallacy

Social stereotypes may be defined as beliefs that various traits or acts are characteristic of particular social groups. As such, stereotypic beliefs represent subjective estimates of the frequencies of attributes within social groups, and so should be expected to “behave like” base-rate information within the context of judgments of individuals: specifically, individuating target case information should induce subjects to disregard their own stereotypic beliefs. Although the results of previous research are consisten with this prediction, no studies have permitted normative evaluation of stereotypic judgments. Because the hypothesis equates base rates and stereotypes, normative evaluation is essential for demonstrating equivalence between the base-rate fallacy and neglect of stereotypes in the presence of individuating case information. Two experiments were conducted, allowing for normative evaluation of effects of stereotypes on judgments of individuals. The results confirmed the hypothesis and established the generalizability of the effect across controversial and uncontroversial, socially desirable and socially underirable stereotypic beliefs. More generally, an examination of the differences between intuitive and normative statistical models of the judgment task suggest that the base-rate fallacy is but one instance of a general characteristic of intuitive judgment processes: namely, the failure to appropriately adjust evaluations of any one cue in the light of concurrent evaluations of other cues.     

The alternative explanation to the alternative‐outcome effect and the detection of the focal outcome effect

Abstract: Previous studies on subjective probability judgment indicate that pair‐wise comparison between the focal and the strongest alternative outcome plays an important role in probability judgment. This study, however, found that the randomness of alternative outcomes affected probability judgment for focal outcome. In the present study, 182 participants provided probability estimates for winning on hypothetical slot machines where both successes and losses were composed of multiple outcomes. The randomness of both the focal and alternative outcomes were defined by the expression used in Rappoport and Budescu (1997 ). The analysis indicated that the more random the distributions of both focal and alternative outcomes, the higher the estimated probability for focal outcome. Some theoretical suggestions are discussed.