Outliers and Influential Observations in Exponential Random Graph Models

We discuss measuring and detecting influential observations and outliers in the context of exponential family random graph (ERG) models for social networks. We focus on the level of the nodes of the network and consider those nodes whose removal would result in changes to the model as extreme or “central” with respect to the structural features that “matter”. We construe removal in terms of two case-deletion strategies: the tie-variables of an actor are assumed to be unobserved, or the node is removed resulting in the induced subgraph. We define the difference in inferred model resulting from case deletion from the perspective of information theory and difference in estimates, in both the natural and mean-value parameterisation, representing varying degrees of approximation. We arrive at several measures of influence and propose the use of two that do not require refitting of the model and lend themselves to routine application in the ERGM fitting procedure. MCMC p values are obtained for testing how extreme each node is with respect to the network structure. The influence measures are applied to two well-known data sets to illustrate the information they provide. From a network perspective, the proposed statistics offer an indication of which actors are most distinctive in the network structure, in terms of not abiding by the structural norms present across other actors.     

Empirical Priors in Polytomous Computerized Adaptive Tests: Risks and Rewards in Clinical Settings

The use of empirical prior information about participants has been shown to substantially improve the efficiency of computerized adaptive tests (CATs) in educational settings. However, it is unclear how these results translate to clinical settings, where small item banks with highly informative polytomous items often lead to very short CATs. We explored the risks and rewards of using prior information in CAT in two simulation studies, rooted in applied clinical examples. In the first simulation, prior precision and bias in the prior location were manipulated independently. Our results show that a precise personalized prior can meaningfully increase CAT efficiency. However, this reward comes with the potential risk of overconfidence in wrong empirical information (i.e., using a precise severely biased prior), which can lead to unnecessarily long tests, or severely biased estimates. The latter risk can be mitigated by setting a minimum number of items that are to be administered during the CAT, or by setting a less precise prior; be it at the expense of canceling out any efficiency gains. The second simulation, with more realistic bias and precision combinations in the empirical prior, places the prevalence of the potential risks in context. With similar estimation bias, an empirical prior reduced CAT test length, compared to a standard normal prior, in 68% of cases, by a median of 20%; while test length increased in only 3% of cases. The use of prior information in CAT seems to be a feasible and simple method to reduce test burden for patients and clinical practitioners alike.     

Latent class analysis of anxiety and depressive symptoms of the Youth Self-Report in a general population sample of young adolescents

This study examined whether distinct groups of young adolescents with mainly anxiety or mainly depression could be identified in a general population sample. Latent class analysis was used on self-report ratings of DSM-IV symptoms of anxiety and depressive disorders, because it was hypothesized that these ratings provide a bigger chance to identify distinct groups than parent ratings of symptoms that are poorly associated with DSM-IV. Results from exploratory and confirmatory latent class analysis showed that only very small numbers of young adolescents had mainly anxiety or mainly depressive symptoms. Instead, a five-group model fitted the data best. These five groups contained young adolescents who either had a high, intermediate, or low probability to have comorbid symptoms of anxiety and depression. It was concluded that symptoms of DSM-IV anxiety and depressive disorders co-occur in young adolescents, and that latent class analysis on items that capture also severe symptoms like suicidal thoughts are needed to derive groups with specific comorbidity patterns in a general population sample.     

Introduction to Michotte's heritage in perception and cognition research

Several decades after Michotte's work was published, it continues to inspire current research in perception, cognition, and beyond. In this special issue we pay tribute to this heritage with a collection of empirical and theoretical papers on amodal completion and the perception of causality, two areas of research within which Michotte's work and ideas have had a lasting influence. As a background to better understand the remaining papers, we briefly sketch Michotte's life and work and the scope (in breadth and in depth) of his impact. We then review Michotte's seminal contributions to the areas covered in this special issue, some of the major research discoveries and themes in the intervening decades, and the major open questions and challenges we are still facing. We also include a sneak preview of the papers in this special issue, noting how they relate to Michotte's work and to each other. This review shows both how much influence Michotte has had on contemporary perception and cognition research, and how much important work remains to be done. We hope that the papers in this special issue will serve both to celebrate Michotte's heritage in this respect, and to inspire other investigators to continue the projects he began.     

Amodal completion and visual holes (static and moving)

Occlusion is a frequent occurrence in a cluttered world of opaque objects. Often information about the shape of partly occluded objects can be gathered from the visible portion of the object and in particular its contours. Here we address the case where a region of a surface is visible exclusively through an aperture (visual hole). We make several observations about the grouping of surface regions visible through holes, and the appearance of moving objects and holes. These observations support the view that holes are shape properties of the object-with-hole.     

Is it impossible to inhibit isoluminant items, or does it simply take longer? Evidence from preview search

Visual search can be facilitated when participants receive a preview of half the distractors (the preview benefit in search; Watson & Humphreys, 1997). Donk and Theeuwes (2001) have argued that preview-based benefits are abolished if the display items are isoluminant to a background. This is consistent with the preview benefit being due to onset capture by the new stimuli. In contrast, the present experiments challenge this suggestion and show that preview benefits can occur under isoluminant conditions, providing that they are given enough time to occur. In Experiment 1, we showed that a preview benefit can occur even with isoluminant stimuli, provided that the old items are previewed for a sufficient time. In Experiment 2, we tested and rejected the idea that this advantage is due to low-level sensory fatigue for the preview stimuli. These findings indicate that the preview effect is not caused solely by onset capture.     

Contextual and Individual Predictors of Psychological Disengagement From Sport During a Competitive Event

The present study aims to identify the processes underlying athletes' psychological disengagement during a competitive event. It was expected that goal attainment would predict psychological disengagement through the mediation of physical self‐worth. It was further hypothesized that athletic identity and passion for the activity would be predictors of psychological disengagement. Athletes completed measures of athletic identity, passion, and physical self‐worth before a competition; and perceived goal attainment, physical self‐worth, and psychological disengagement after a competition. Physical self‐worth mediated the relationship between perceived goal attainment and discounting. Obsessive passion and athletic identity were negatively related to devaluing over and above goal attainment and physical self‐worth. The study highlights individual and contextual correlates of psychological disengagement in the sport setting.