Symmetry as a method of proof

This paper is a logical study of valid uses of symmetry in deductive reasoning, of what underlying principles make some appeals to symmetry legitimate but others illegitimate. The issue is first motivated informally. A framework is then given covering a fairly broad range of symmetry arguments, and the formulation of symmetry provided is shown to be a valid principle of reasoning, as is a slightly stronger principle of reasoning, one that is shown to be in some sense as strong as possible. The relationship between symmetry and isomorphism is discussed, and finally the framework is extended to a more general model-theoretic setting.     

TEACHER POPULARITY AND CONTRAST EFFECTS IN A CLASSROOM TOKEN ECONOMY

There is a common fear that the use of a token economy in one classroom might harm pupil performance in situations where the contingencies are not in effect. This study investigated potential contrast effects on measures of children's productivity and attitudes toward teachers. Six children with reading deficits participated. A multiple baseline design was used to assess the effects of a token economy which was systematically introduced across three teachers. Dependent measures included two rating forms of teacher popularity and work rate on a programmed reading series. The results indicated that the token system was effective in increasing the children's productivity and that no consistent behavioral contrast effects occurred. Furthermore, children's attitudes toward teachers did not appear to be influenced by the token economy until only one teacher was not delivering tokens. At this point, her popularity declined until she also delivered tokens. The token economy manipulation appeared to have a specific, desirable effect on the targeted behavior (i.e., work rate) and had minimal negative or positive “side effects” on teacher popularity.     

An experimental space combining individual and social performances

This report describes several primate environments in which two or more animals shared a common social area. Automatic programming was used to permit concurrent individual sessions. Some of the behavioral phenomena observed in these environments, including reinforcing properties of social interactions, are discussed.     

Methodological challenges in union commitment studies

Methodological problems in studies of union commitment were identified and illustrated with data from 4,641 members and 479 stewards in 297 local teachers' unions. Using a 20-item union commitment scale, results confirmed the existence of 3 substantive factors and 1 method factor at the individual level of analysis: loyalty to the union, responsibility to the union, willingness to work for the union, and a factor of negatively worded items. Tests of measurement invariance showed that the scale captured commitment for rank-and-file members but not for union stewards. The authors also found partial measurement invariance between long-time and newer members and full measurement invariance between men and women. Finally, the authors found that violation of the statistical assumption of independence reduced model fit when individual commitment scores were analyzed without attention to the hierarchical nature of the data.     

Inequality constrained analysis of variance: a Bayesian approach

Researchers often have one or more theories or expectations with respect to the outcome of their empirical research. When researchers talk about the expected relations between variables if a certain theory is correct, their statements are often in terms of one or more parameters expected to be larger or smaller than one or more other parameters. Stated otherwise, their statements are often formulated using inequality constraints. In this article, a Bayesian approach to evaluate analysis of variance or analysis of covariance models with inequality constraints on the (adjusted) means is presented. This evaluation contains two issues: estimation of the parameters given the restrictions using the Gibbs sampler and model selection using Bayes factors in the case of competing theories. The article concludes with two illustrations: a one-way analysis of covariance and an analysis of a three-way table of ordered means.     

Children's perception of media-portrayed sex roles

The immediate impact on preschool and elementary school children of a televised presentation in which the traditional sex roles of physician and nurse were reversed was examined. After viewing a videotape of a male nurse and a female physician, subjects were asked to identify photographs or names of the physician and nurse. Preschool, first-, and fourth-grade children selected male names or pictures for the physician and female names or pictures for the nurse, thereby reversing genders. Their immediate recall appeared strongly influenced by their stereotypes rather than by the film they had just viewed. Seventh-grade children correctly identified the names of the physician and nurse.The authors wish to thank Dr. Edward F. Meydrech, Assistant Professor, Department of Preventive Medicine and Chief of the Division of Biostatistics, University of Mississippi Medical Center, for his invaluable assistance in the analysis of the data.     

The phenotypic consequences of MECP2 mutations extend beyond Rett syndrome

Although MECP2 was initially identified as the causative gene in classic Rett syndrome (RTT), the gene has now been implicated in several phenotypes that extend well beyond the clinically defined disorder. MECP2 mutations have been found in people with various disorders, including neonatal onset encephalopathy, X-linked recessive mental retardation (MRX), classic and atypical RTT, autism, and Angelman syndrome, as well as mildly affected females and normal carrier females. To make matters more complex, in approximately 20% of classic sporadic RTT cases and more than 50% of affected sister pairs, no mutation in MECP2 has been found. X-chromosome inactivation patterns can clearly affect the phenotypic expression in females, while the effect of the type and position of the mutation is more apparent in the broader phenotype than in RTT. Both males and females are at risk, although an excess of paternally derived mutations are found in most cases of classic RTT. Thus, because of the range of disparate phenotypes, the gene may account for a relatively large portion of mental retardation in the population.