Missing data: our view of the state of the art

Statistical procedures for missing data have vastly improved, yet misconception and unsound practice still abound. The authors frame the missing-data problem, review methods, offer advice, and raise issues that remain unresolved. They clear up common misunderstandings regarding the missing at random (MAR) concept. They summarize the evidence against older procedures and, with few exceptions, discourage their use. They present, in both technical and practical language, 2 general approaches that come highly recommended: maximum likelihood (ML) and Bayesian multiple imputation (MI). Newer developments are discussed, including some for dealing with missing data that are not MAR. Although not yet in the mainstream, these procedures may eventually extend the ML and MI methods that currently represent the state of the art.     

Development of an Infrequency-Psychopathology scale for the MMPI-A: the Fp-A Scale

This article describes the development and initial validation of the Infrequency-Psychopathology scale, Fp-A, for the MMPI-A (Butcher et al., 1992). The scale parallels the Infrequency-Psychopathology scale, F(p), that has been developed for the MMPI-2 (Butcher, Dahlstrom, Graham, Tellegen, & Kaemmer, 1989). Results demonstrated that the 40-item Fp-A scale is superior to the F scale at discriminating between faking-bad and accurate reports of psychopathology, although the improvement over F was modest, particularly when compared to the improvement found for the F(p) scale. The difference seemed to reflect the superiority of the MMPI-A F scale to the MMPI-2 F scale. Even so, the findings suggest that the identification of overreporting on the MMPI-A could potentially be enhanced by using Fp-A as an adjunct to the F scale.     

Separate roles for executive and phonological components of working memory in mental arithmetic

A dual-task methodology was used to investigate the roles played by executive and phonological aspects of working memory in mental arithmetic. Experiment 1 showed that suppression of articulation impaired the ability to add a pair of briefly presented three-digit numbers. Suppression had no effect when the need to store temporarily was minimized by making the numbers visible throughout calculation. Experiment 2 showed that disrupting executive processes by requiring concurrent performance of a Trails task impaired the ability to add numbers that remained permanently visible. Performance on the Trails task deteriorated as the number of carry operations in the addition increased. Experiment 3 showed that this decline in Trails performance was not simply due to the extra time taken by carrying. These and other features of the results suggest that the carrying component of mental arithmetic places substantial demands on executive processes, whereas the need to retain problem information is met by the phonological loop. The results are consistent with an interpretation of executive processes according to which there is a limit on the capacity to inhibit strongly primed routine operations.     

On the interpretation of working memory span in adults

Experimental research into children's working memory span has shown that retention duration contributes substantially to span performance, while processing efficiency need not be related to concurrent memory load (Towse, Hitch, & Hutton, 1998). These findings have been used to argue for a model of working memory span that emphasizes time-based forgetting rather than the popular resource-sharing or tradeoff framework. The present paper considers whether adults perform working memory span tasks in a qualitatively different way. Data from reading span and operation span tasks show that adults' performance can be distinguished from that of children, but also that a task-switching model of working memory span can explain some important aspects of performance.     

From Four‐ to Five‐Dimensionalism

Philosophers have long noticed the similarity of identity over time and identity across worlds. Despite this similarity, analogous views on these matters are not always taken equally seriously. Four‐dimensionalism is one of the most well‐known accounts of identity over time. There is a clear modal analogue of four‐dimensionalism, on which objects are modally extended and their trans‐world identity is a matter of having distinct modal parts located in different possible worlds. Yet this view, which we might call ‘five‐dimensionalism,’ is rarely discussed or defended, in comparison to its temporal counterpart. I argue that five‐dimensionalism is at least as plausible as four‐dimensionalism and deserves serious consideration as an account of trans‐world identity. The strategy is to show that arguments typically used in defence of four‐dimensionalism can be adapted to defend five‐dimensionalism as well. A powerful consideration in favour of four‐dimensionalism is the fact that it provides an elegant and unified solution to a variety of puzzles concerning material coincidence. I show that such puzzles come in equally troubling modal varieties and that five‐dimensionalism provides an equally unified and elegant solution to them. 1     

The Role of Semantic Clustering in Optimal Memory Foraging

Recent studies of semantic memory have investigated two theories of optimal search adopted from the animal foraging literature: Lévy flights and marginal value theorem. Each theory makes different simplifying assumptions and addresses different findings in search behaviors. In this study, an experiment is conducted to test whether clustering in semantic memory may play a role in evidence for both theories. Labeled magnets and a whiteboard were used to elicit spatial representations of semantic knowledge about animals. Category recall sequences from a separate experiment were used to trace search paths over the spatial representations of animal knowledge. Results showed that spatial distances between animal names arranged on the whiteboard were correlated with inter‐response intervals (IRIs) during category recall, and distributions of both dependent measures approximated inverse power laws associated with Lévy flights. In addition, IRIs were relatively shorter when paths first entered animal clusters, and longer when they exited clusters, which is consistent with marginal value theorem. In conclusion, area‐restricted searches over clustered semantic spaces may account for two different patterns of results interpreted as supporting two different theories of optimal memory foraging.