The statistical theory of stepped-up reliability coefficients when a test has been divided into several equivalent parts

This paper is a presentation of the statistical sampling theory of stepped-up reliability coefficients when a test has been divided into any number of equivalent parts. Maximum-likelihood estimators of the reliability are obtained and shown to be biased. Their sampling distributions are derived and form the basis of the definition of new unbiased estimators with known sampling distributions. These unbiased estimators have a smaller sampling variance than the maximum-likelihood estimators and are, because of this and some other favorable properties, recommended for general use. On the basis of the variances of the unbiased estimators the gain in accuracy in estimating reliability connected with further division of a test can be expressed explicitly. The limits of these variances and thus the limits of accuracy of estimation are derived. Finally, statistical small sample tests of the reliability coefficient are outlined. This paper also covers the sampling distribution of Cronbach's coefficient alpha.     

The impact of enhanced incentives on vocational rehabilitation outcomes for dually diagnosed veterans

This study evaluated the efficacy of adding contingency management techniques to vocational rehabilitation (VR) to improve treatment outcome as measured by entry into competitive employment. Nineteen dually diagnosed veterans who entered VR in the Veterans' Administration's compensated work therapy (CWT) program were randomly assigned to CWT (n = 8) or to CWT with enhanced incentives (n = 11). Over the first 16 weeks of rehabilitation, those in the incentives condition could earn up to dollar 1,006 in cash for meeting two sets of clinical goals: (a) remaining abstinent from drugs and alcohol and (b) taking steps to obtain and maintain a competitive job. Results indicate that relative to participants in the CWT-only group, those in the incentives condition engaged in more job-search activities, were more likely to remain abstinent from drugs and alcohol, were more likely to obtain competitive employment, and earned an average of 68% more in wages. These results suggest that rehabilitation outcomes may be enhanced by restructuring traditional work-for-pay contingencies to include direct financial rewards for meeting clinical goals.     

Postural stability and hand preference as constraints on one-handed catching performance in children

Effects of postural state and hand preference as constraints on 1-handed catching performance were investigated in different ability groups of children aged 9-10 years. On the basis of pretest data, the authors classified 48 participants into groups of good, intermediate, and poor catchers (n = 16 in each) and asked them to perform 1-handed catches with their preferred and nonpreferred hands while standing and sitting. The good catchers' performance was not affected by the imposed postural constraints but did improve when they used the preferred hand. A similar effect of hand preference was evident in the intermediate and poor catchers, but there was also an effect of postural constraint. Independent of hand preference, intermediate catchers' performance while seated improved significantly compared with that during standing. For poor catchers, there was an interaction between hand preference and posture; significant improvement was evident only when they used the preferred hand in the sitting condition. The finding that manipulation of posture and hand preference affected performance outcomes indicates that perceptual skill is not the only influence on catching performance in children. Manipulation of those key constraints may facilitate the acquisition of catching skill, but more research is needed to determine the permanence of those effects.     

Self-enhancement among high-exposure survivors of the September 11th terrorist attack: resilience or social maladjustment?

The authors examined self-enhancing bias as a predictor of adjustment among individuals in or near the World Trade Center during the September 11, 2001, terrorist attacks. Resilience was defined from categorical and continuous analyses of both participant self-report and friend and relative ratings of adjustment. Self-enhancement was associated with a resilient outcome, ratings of better adjustment prior to September 11th, greater positive affect, and reduced perceptions of social constraints. Additional analyses indicated that self-enhancers' reduced symptom levels were fully mediated by their low perceived social constraints. However, consistent with previous evidence suggesting a social cost to self-enhancement, at 18 months post-September 11th, self-enhancers' friends and relatives also rated them as decreasing in social adjustment and as being less honest.     

Effect of orienting the finger opposition space in the control of reach-to-grasp movements

Participants (N = 13) made reach-to-grasp movements to an elongated object with or without a forearm pronation movement. Grasp and transport components of movements performed without forearm pronation differed from those performed when participants preplanned forearm pronation. The transport distance traveled after peak aperture (aperture closure distance) was unchanged, however, suggesting that participants initiated aperture closure on the basis of the distance of the hand from the target. When they suddenly pronated the forearm in response to a perturbation, aperture kinematics were altered from a monophasic to a biphasic profile and aperture closure distance was shortened. Conversely, a sudden reorientation to a nonpronated position minimized those changes. Thus, the relationship between transport and aperture components is differentially altered depending on online reorientation of the forearm.     

Neural correlates of a default response in a delayed go/no-go task

Working memory, the ability to temporarily retain task-relevant information across a delay, is frequently investigated using delayed matching-to-sample (DMTS) or delayed Go/No-Go tasks (DGNG). In DMTS tasks, sample cues instruct the animal which type of response has to be executed at the end of a delay. Typically, performance decreases with increasing delay duration, indicating that working memory fades across a delay. However, no such performance decrease has been found when the sample cues exist of present vs. absent stimuli, suggesting that pigeons do not rely on working memory, but seem to respond by default in those trials. We trained 3 pigeons in a DGNG task and found a similar default response pattern: The diverging slopes of the retention functions on correct Go and No-Go trials suggested that pigeons by default omitted their response following No-Go stimuli, but actively retained task-relevant information across the delay for successful responses on Go trials. We conducted single-cell recordings in the avian nidopallium caudolaterale, a structure comparable to the mammalian prefrontal cortex. On Go trials, many neurons displayed sustained elevated activity during the delay preceding the response, replicating previous findings and suggesting that task-relevant information was neurally represented and maintained across the delay. However, the same units did not show enhanced delay activity preceding correct response suppressions in No-Go trials. This activation-inactivation pattern presumably constitutes a neural correlate of the default response strategy observed in the DGNG task.