Exact and resampling probability values for measures of categorical variation and consensus

When analyzing categorical data, it is often important to assess the magnitude of variation, or consensus, among observations in unordered categories. Utilizing the theory of partitions, exact solutions for five commonly used measures of categorical variation are presented. When the number of partitions is very large, resampling methods provide close approximations to exact probability values.     

Resampling probability values for differences between two independent indices of ordinal variation and consensus

A permutation method is presented to calculate resampling probability values for differences between two independent indices of ordinal variation and consensus.     

Projecting group liking and ethnocentrism on in-group members: False consensus effect of attitude strength

The purpose of the present study was to examine the social projection effect concerning the strength of national attitudes. Japanese respondents sampled from the general population judged how patriotic and nationalistic opinions were distributed among Japanese (i.e. in-group) and American (out-group) citizens. The respondents' own positions regarding these attitude dimensions were also measured. As predicted, the respondents inflated estimates of the endorsement for positions close to their own, particularly when the target was the in-group. Estimates of opinion distributions in the out-group converged around stereotypic positions. The apparent projection effect in patriotism (i.e. in-group liking) was likely mediated by abstract trait evaluations of the home country, while the projection of nationalism (i.e. ethnocentrism) appeared to be a direct result of projection without such mediation. Different processes such as the motivation for cognitive consistency and the need to achieve social identity of the group were suggested to underlie projection effects in different domains. Implications of the results for the study of stereotyping and intergroup conflict are discussed.     

Effect of group heterogeneity on item parameters

Most indexes of item validity and difficulty vary systematically with changes in the mean and variance of the group. Formulas are presented showing how certain item parameters will vary with these alterations in group mean and variance. Item parameters are also suggested which should remain invariant under such changes. These parameters are developed under two different assumptions: first, the assumption that thetotal distribution of the item ability variable is normal, and, second, that the distribution of the item ability variablefor each array of the explicit selection variable is normal. The writer wishes to acknowledge helpful discussions of this paper with Paul Horst and Herbert S. Sichel who have worked on various aspects of the problem of invariant item parameters.     

Transactive memory in organizational groups: the effects of content, consensus, specialization, and accuracy on group performance

Previous research on transactive memory has found a positive relationship between transactive memory system development and group performance in single project laboratory and ad hoc groups. Closely related research on shared mental models and expertise recognition supports these findings. In this study, the author examined the relationship between transactive memory systems and performance in mature, continuing groups. A group's transactive memory system, measured as a combination of knowledge stock, knowledge specialization, transactive memory consensus, and transactive memory accuracy, is positively related to group goal performance, external group evaluations, and internal group evaluations. The positive relationship with group performance was found to hold for both task and external relationship transactive memory systems.     

Democracy justifies the means: political group structure moderates the perceived legitimacy of intergroup aggression

The present research tested the hypothesis that the political structure of conflicting groups moderates perceived legitimacy of intergroup aggression. In two experiments, participants read scenarios of fictitious summer camps in which members of one group aggressed members of another group. The political structure of both the perpetrator and the victim groups was described as either egalitarian (defined with democratic decision-making procedures) or hierarchical (authoritarian decision-making procedures). Results of both experiments showed that aggressions perpetrated by members of egalitarian groups at the expense of members of hierarchical groups were evaluated as less illegitimate than aggressions committed in the three remaining conditions. This effect is discussed as a function of the higher social value attributed to democratic groups.     

Effect of depression on processing interactions in group psychotherapy

Two studies were conducted to investigate the possibility of individual differences in the ability of inpatients to process interactions in group psychotherapy. The first was a pilot study conducted on groups of major depressive patients and matched normal subjects. Subjects were asked to give process comments after viewing simulations of typical group therapy interactions. These comments were later rated on the extent to which they reflected process qualities and accuracy. These data led to a more rigorous and extensive study that included more appropriate control groups as well as measures of potential confounding factors, such as simulation realism, verbal ability, and interaction comprehension. Results indicated that major depressives suffer from deficits in the ability to process group interactions, relative to three types of control groups, including normals. These differences in processing were not significantly positively correlated with any of the potential confounding factors. The implications for understanding interactional processing and group psychotherapy are discussed.     

Shafer on conditional probability

Journal of Philosophical Logic -     

In-vivo rating of treatment acceptability by children: Effects of probability instruction on student's spelling performance under group contingency conditions

In prior studies, Shapiro and Goldberg (1986, 1990) failed to find a relationship between in-vivo ratings by children of treatment acceptability and treatment effectiveness. These studies involved the use of interdependent and dependent group contingencies designed to improve the spelling performance of sixth grade students. To investigate whether the failure to link treatment acceptability and effectiveness may have been due to the subjects' inability to understand the differences in treatment conditions, this study utilized a pre-intervention training package to enhance salient differences between two types of group contingencies. Results of this study showed that both group contingencies were successful at improving the spelling performance of students, particularly the poorer spellers. Prior to treatment, students preferred the interdependent condition, with the higher-achieving students expressing the strongest preference. After implementation of the training package, both conditions were now rated as equally acceptable. Pre- and post-test acceptability ratings of each condition tended to be significantly correlated but correlations between acceptability ratings and treatment effectiveness were negligible at all points in the study. Limitations of the present study and suggestions for further research are discussed.     

The role of diagnosticity in stereotype formation: perceiving group means and variances.

Three experiments tested the hypotheses that while forming stereotypes of social groups, people abstract the central tendency and variability of different attribute dimensions to determine which ones best differentiate the groups and that more differentiating dimensions are more likely to become stereotypical in the sense of becoming strongly associated with the groups in memory. Supporting these hypotheses. Experiment 1 found that, after viewing behaviors performed by members of 2 groups, Ss characterized the groups more in terms of attribute dimensions indicating larger differences between the central tendencies of the groups, and Experiment 2 showed that this effect did not occur when Ss formed impressions of only 1 group. Experiment 3 found that Ss also characterized groups more in terms of attribute dimensions indicating lower within-group variability.     

Pollock on probability in epistemology

In Thinking and Acting John Pollock offers some criticisms of Bayesian epistemology, and he defends an alternative understanding of the role of probability in epistemology. Here, I defend the Bayesian against some of Pollock's criticisms, and I discuss a potential problem for Pollock's alternative account.