Weight matrices for social influence analysis: An investigation of measurement errors and their effect on model identification and estimation quality

Weight matrices, such as used in network autocorrelation models, are useful to investigate social influence processes. The objective of this paper is to investigate a key topic that has received relatively little attention in previous research, namely the issues that arise when observational limitations lead to measurement errors in these weight matrices. Measurement errors are investigated from two perspectives: when relevant ties are omitted, and when irrelevant ties are erroneously included as part of the matrix. The paper first shows analytically that these two situations result in biased estimates. Next, a simulation experiment provides evidence of the effect of erroneously coding the weight matrix on model performance and the ability of a network autocorrelation test to identify social influence effects. The results suggest that depending on the level of autocorrelation and the topology attributes of the underlying matrix, there is a window of opportunity to identify and model social influence processes even in situations where the ties in a matrix cannot be accurately observed.     

Prenatal Development of Interlimb Motor Learning in the Rat Fetus

The role of sensory feedback in the early ontogeny of motor coordination remains a topic of speculation and debate. On E20 of gestation (the 20th day after conception, 2 days before birth), rat fetuses can alter interlimb coordination after a period of training with an interlimb yoke, which constrains limb movement and promotes synchronized, conjugate movement of the yoked limbs. The aim of this study was to determine how the ability to express this form of motor learning may change during prenatal development. Fetal rats were prepared for in vivo study at 4 ages (E18–21) and tested in a 65‐min training‐and‐testing session examining hind limb motor learning. A significant increase in conjugate hind limb activity was expressed by El9, but not El 8 fetuses, with further increases in conjugate hind limb activity on E20 and E21. These findings suggest substantial development of the ability of fetal rats to modify patterns of interlimb coordination in response to kinesthetic feedback during motor training before birth.     

Emerging organizational forms: Work and organization in the 21st century

This article begins with the premise that there is continuous and accelerating change in the Western World in the nature of work and how it is organized. An important contributory force is information technology — itself changing rapidly.When the dynamics of the external environment of organizations are added to changes in IT, we will see new forms of organizations evolving in the business world, such as the ‘starburst’ and ‘internal market’ structures.Michael Scott Morton supplies a diagram to illustrate the framework of research which the ‘1990s’ program at MIT is following — how to balance the dynamic tension between external forces and the internal dimensions of organizations to reward shareholders adequately. He refers to one of Peter Senge's ideas in The Fifth Dimension which is central in creating an organization which learns how to innovate constantly: System Thinking — the search for systemic patterns. It reinforces Scott Morton's argument, and seems a particularly appropriate discipline in a continuously turbulent business environment.     

Gender differences in the initiation and attribution of tactile intimacy

Cultural norms may restrict the demonstration of intimacy between men, such that male adults are relatively unlikely (in comparison to females) to display affection in public by hugging or putting hands around one another's waists. Study 1 examined via a role playing technique how the gender composition of a dyad and types of friendship influence tactile greetings. Males displayed less physical intimacy with male friends than with female (platonic or dating) friends and less than females displayed with their same-sex friends. Study 2 examined subjects' perceptions of and attributions about reciprocal touch. Male-male behavior was rated as less normal as a function of the level of physical touch (going from no touch, hugging, to arms around the waist). The normalcy rating of opposite-sex pairs did not vary as a function of the touch manipulation, but female, same-sex pairs' behavior was rated as less normal in the arms around the waist than in either the no touch or hug conditions. In the male same-sex pairs, hugging was seen as more likely to reflect a sexual relationship than no touch, while arms around one another's waist was rated as even more likely to represent a sexual relationship. It was suggested that homophobia, the fear of appearing or being homosexual, may operate to inhibit physical intimacy between men.     

Confidence regions for the common mean vector of several multivariate normal populations

Suppose that there are independent samples available from several multivariate normal populations with the same mean vector m? but possibly different covariance matrices. The problem of developing a confidence region for the common mean vector based on all the samples is considered. An exact confidence region centered at a generalized version of the well-known Graybill-Deal estimator of m? is developed, and a multiple comparison procedure based on this confidence region is outlined. Necessary percentile points for constructing the confidence region are given for the two-sample case. For more than two samples, a convenient method of approximating the percentile points is suggested. Also, a numerical example is presented to illustrate the methods. Further, for the bivariate case, the proposed confidence region and the ones based on individual samples are compared numerically with respect to their expected areas. The numerical results indicate that the new confidence region is preferable to the single-sample versions for practical use.     

Development of a Standard Soil-to-Skin Adherence Probability Density Function for Use in Monte Carlo Analyses of Dermal Exposure

It has recently been suggested that "standard" data distributions for key exposure variables should be developed wherever appropriate for use in probabilistic or "Monte Carlo" exposure analyses. Soil-on-skin adherence estimates represent an ideal candidate for development of a standard data distribution: There are several readily available studies which offer a consistent pattern of reported results, and more importantly, soil adherence to skin is likely to vary little from site-to-site. In this paper, we thoroughly review each of the published soil adherence studies with respect to study design, sampling, and analytical methods, and level of confidence in the reported results. Based on these studies, probability density functions (PDF) of soil adherence values were examined for different age groups and different sampling techniques. The soil adherence PDF developed from adult data was found to resemble closely the soil adherence PDF based on child data in terms of both central tendency (mean = 0.49 and 0.63 mg-soil/cm²-skin, respectively) and 95th percentile values (1.6 and 2.4 mg-soil/cm²-skin, respectively). Accordingly, a single, "standard" PDF is presented based on all data collected for all age groups. This standard PDF is lognormally distributed; the arithmetic mean and standard deviation are 0.52 ± 0.9 mg-soil/cm²-skin. Since our review of the literature indicates that soil adherence under environmental conditions will be minimally influenced by age, sex, soil type, or particle size, this PDF should be considered applicable to all settings. The 50th and 95th percentile values of the standard PDF (0.25 and 1.7 mg-soil/cm²-skin, respectively) are very similar to recent U.S. EPA estimates of "average" and "upper-bound" soil adherence (0.2 and 1.0 mg-soil/cm²-skin, respectively).     

Passed over for promotion because of age: An empirical analysis of the consequences

I test whether older individuals who report that their firms favor younger workers in promotion decisions are harmed by this oftencited discriminatory practice. Using the Health and Retirement Study, I determine whether such workers are more likely to experience lower wage growth, to separate from their employer, or to retire early, in comparison with workers with similar demographic and job characteristics. The evidence is consistent with lower wage growth and a greater likelihood of early retirement. Much of the effect, however, is likely to stem from a high correlation between delayedpayment contracts and promotion practices. I thank Jeff Biddle, John Goddeeris, David Neumark, John Strauss, and Jeff Wooldridge for helpful comments and suggestions. I gratefully acknowledge fellowship support during the completion of this paper from the Robert Wood Johnson Foundation.