Sex Differences in Infants' Ability to Represent Complex Event Sequences

Prior research suggests that when very simple event sequences are used, 4.5‐month‐olds demonstrate the ability to individuate objects based on the continuity or disruption of their speed of motion (Wilcox & Schweinle, 2003). However, infants demonstrate their ability to individuate objects in an event‐monitoring task (i.e., infants must keep track of an ongoing event) at a younger age than in an event‐mapping task (i.e., infants must compare information from 2 different events). The research presented here built on these findings by examining infants' capacity to succeed on an event‐mapping task with a more complex event sequence to determine if the complexity of the event interferes with their ability to form summary representations of the event, and, in short, individuate the objects. Three experiments were conducted with infants 4.5 to 9.5 months of age. The results indicated that (a) increasing the complexity of the objects' trajectories adversely affected infants' performance on the task, and (b) boys were more likely to succeed than girls. These findings shed light on how representational capacities change during the first year of life and are discussed in terms of information processing and representational capabilities as well as neuro‐anatomical development.     

A comparison of six smoothers when there are multiple predictors

The paper compares six smoothers, in terms of mean squared error and bias, when there are multiple predictors and the sample size is relatively small. The focus is on methods that use robust measures of location (primarily a 20% trimmed mean) and where there are four predictors. To add perspective, some methods designed for means are included. The smoothers include the locally weighted (loess) method derived by Cleveland and Devlin [W.S. Cleveland, S.J. Devlin, Locally-weighted regression: an approach to regression analysis by local fitting, Journal of the American Statistical Association 83 (1988) 596–610], a variation of a so-called running interval smoother where distances from a point are measured via a particular group of projections of the data, a running interval smoother where distances are measured based in part using the minimum volume ellipsoid estimator, a generalized additive model based on the running interval smoother, a generalized additive model based on the robust version of the smooth derived by Cleveland [W.S. Cleveland, Robust locally weighted regression and smoothing scatterplots, Journal of the American Statistical Association 74 (1979) 829–836], and a kernel regression method stemming from [J. Fan, Local linear smoothers and their minimax efficiencies, The Annals of Statistics 21 (1993) 196–216]. When the regression surface is a plane, the method stemming from [J. Fan, Local linear smoothers and their minimax efficiencies, The Annals of Statistics 21 (1993) 196–216] was found to dominate, and indeed offers a substantial advantage in various situations, even when the error term has a heavy-tailed distribution. However, if there is curvature, this method can perform poorly compared to the other smooths considered. Now the projection-type smoother used in conjunction with a 20% trimmed mean is recommended with the minimum volume ellipsoid method a close second.     

BUSY PLACES AND BROKEN WINDOWS? Toward Defining the Role of Physical Structure and Process in Community Crime Models

Borrowing from the systemic model of social disorganization theory as well as from theories of human ecology and urban geography, we examine the effects of land use on community rates of violence and burglary. We posit that community crime is differentially affected by distinct nonresidential physical spaces in a neighborhood—distinct in terms of whether they are adult-centered, "business-oriented" public spaces versus spaces that are public yet still "resident centered," especially toward community youth (e.g., educational and recreational spaces). We examine potential main, mediating, and moderating effects of neighborhood social structure, resident-centered versus business-oriented public land use, and neighborhood-level processes, including neighboring and physical incivility, using data from 100 Seattle census tracts. Results suggest that the effects of schools on community violence are largely direct, while the effect of business places on violent crime is mediated substantially, but not completely, by physical disorder. In contrast, the effect of playgrounds on violence is moderated by residential instability. Regarding burglary, presence of schools is nonsignificant. Presence of businesses increases burglary, though the effect is partially mediated again by physical disorder. The effect of businesses is also moderated by residential (in)stability. Presence of playgrounds increases burglary risk regardless of neighborhood social-structural characteristics.     

Post-hoc analyses in multiple regression based on prediction error

A well-known problem in multiple regression is that it is possible to reject the hypothesis that all slope parameters are equal to zero, yet when applying the usual Student's T-test to the individual parameters, no significant differences are found. An alternative strategy is to estimate prediction error via the 0.632 bootstrap method for all models of interest and declare the parameters associated with the model that yields the smallest prediction error to differ from zero. The main results in this paper are that this latter strategy can have practical value versus Student's T; replacing squared error with absolute error can be beneficial in some situations and replacing least squares with an extension of the Theil-Sen estimator can substantially increase the probability of identifying the correct model under circumstances that are described.     

On a lottery pricing anomaly: Time tells the tale

This article identifies a lottery pricing anomaly, which I call the “r=x anomaly,” that is present in past pricing experiments—namely, a tendency for subjects to announce that their minimum selling price for some binary lottery is the greater of the two lottery prizes. The study shows that the anomaly is inconsistent with two theoretical explanations for another well-known pricing anomaly (preference reversal) and experimentally replicates these inconsistencies. The new experiment also measures the time subjects spend making their pricing decisions. These decision-time measurements suggest that ther=x anomaly may be a decision-cost effect.     

WEAPONS AT SCHOOL: ARE THE PREDICTORS GENERALIZABLE ACROSS CONTEXT?

This study addresses the reasons for school-based weapon carrying across three diverse county-level contexts. Weapon carrying among students at school has been, until very recently, neglected in research. Further, much of the information that is available is non-comparative. Hence, whether the etiology of in-school weapon carrying is generalizable across diverse settings remains largely an unanswered question. The present study moves toward a test of generalizability by comparing student weapon possession and its antecedents in three geographically, economically, and culturally distinct communities in Kentucky. Findings suggest that few differences exist across context regarding the etiology of school-based weapon carrying. Regardless of community context, peer weapon carrying as well as criminal lifestyle are important predictors of adolescents carrying weapons to school.